setlocale: improve fallback on macOS

[Bruno Haible]

On macOS, the setlocale override that I added produces warnings such as
  Warning: Failed to set locale category LC_NUMERIC to fr_DE.
  Warning: Failed to set locale category LC_TIME to fr_DE.
  Warning: Failed to set locale category LC_COLLATE to fr_DE.
  Warning: Failed to set locale category LC_MONETARY to fr_DE.
  Warning: Failed to set locale category LC_MESSAGES to fr_DE.
when I set my preferences (in the system's preferences dialog) to
  - a languages preferences list that has French as first preference,
  - a territory = Germany.

The reason is that when language and territory can be chosen independently,
the resulting locale (here fr_DE) does not exist on the system.

With this patch, I'm improving things such that
1)
  - for the first 4 categories, de_DE will be used instead of fr_DE
    (because it's a reasonable assumption that these locale categories
    depend mainly on the territory),
  - for LC_MESSAGES, fr_FR will be used instead of fr_DE, and thus gettext
    will open the message catalogs for 'fr',
This does not cover all cases, only those where locales exist on the system.
For instance, when the user chooses Herero language or Liberia territory,
the system does not have such a locale, and these improved heuristics won't
help.

2)
  - the warnings will only appear when the environment variable
    SETLOCALE_VERBOSE is set to a non-empty value - so that output to stderr
    is avoided by default.


2019-05-20  Bruno Haible  <address@hidden>

        setlocale: Improve fallback on macOS.
        * lib/setlocale.c (search): Optimize away a redundant strcmp()
        invocation.
        (locales_with_principal_territory): New array.
        (langcmp, get_main_locale_with_same_language): New functions.
        (locales_with_principal_language): New array.
        (terrcmp, get_main_locale_with_same_territory): New functions.
        (rpl_setlocale): When setlocale_single failed, try again with a locale
        that is more likely to exist. Don't warn if the environment variable
        SETLOCALE_VERBOSE is not set.

diff --git a/lib/setlocale.c b/lib/setlocale.c
index e14805e..fbabe99 100644
--- a/lib/setlocale.c
+++ b/lib/setlocale.c
@@ -617,7 +617,7 @@ search (const struct table_entry *table, size_t table_size, 
const char *string,
           {
             size_t i;
 
-            for (i = mid; i < hi; i++)
+            for (i = mid + 1; i < hi; i++)
               {
                 if (strcmp (table[i].code, string) > 0)
                   {
@@ -857,6 +857,527 @@ setlocale_single (int category, const char *locale)
 #  define setlocale_single setlocale_unixlike
 # endif
 
+# if defined __APPLE__ && defined __MACH__
+
+/* Mapping from language to main territory where that language is spoken.  */
+static char const locales_with_principal_territory[][6 + 1] =
+  {
+                /* Language     Main territory */
+    "ace_ID",   /* Achinese     Indonesia */
+    "af_ZA",    /* Afrikaans    South Africa */
+    "ak_GH",    /* Akan         Ghana */
+    "am_ET",    /* Amharic      Ethiopia */
+    "an_ES",    /* Aragonese    Spain */
+    "ang_GB",   /* Old English  Britain */
+    "arn_CL",   /* Mapudungun   Chile */
+    "as_IN",    /* Assamese     India */
+    "ast_ES",   /* Asturian     Spain */
+    "av_RU",    /* Avaric       Russia */
+    "awa_IN",   /* Awadhi       India */
+    "az_AZ",    /* Azerbaijani  Azerbaijan */
+    "ban_ID",   /* Balinese     Indonesia */
+    "be_BY",    /* Belarusian   Belarus */
+    "bej_SD",   /* Beja         Sudan */
+    "bem_ZM",   /* Bemba        Zambia */
+    "bg_BG",    /* Bulgarian    Bulgaria */
+    "bho_IN",   /* Bhojpuri     India */
+    "bi_VU",    /* Bislama      Vanuatu */
+    "bik_PH",   /* Bikol        Philippines */
+    "bin_NG",   /* Bini         Nigeria */
+    "bm_ML",    /* Bambara      Mali */
+    "bn_IN",    /* Bengali      India */
+    "bo_CN",    /* Tibetan      China */
+    "br_FR",    /* Breton       France */
+    "bs_BA",    /* Bosnian      Bosnia */
+    "bug_ID",   /* Buginese     Indonesia */
+    "ca_ES",    /* Catalan      Spain */
+    "ce_RU",    /* Chechen      Russia */
+    "ceb_PH",   /* Cebuano      Philippines */
+    "co_FR",    /* Corsican     France */
+    "cr_CA",    /* Cree         Canada */
+    /* Don't put "crh_UZ" or "crh_UA" here.  That would be asking for fruitless
+       political discussion.  */
+    "cs_CZ",    /* Czech        Czech Republic */
+    "csb_PL",   /* Kashubian    Poland */
+    "cy_GB",    /* Welsh        Britain */
+    "da_DK",    /* Danish       Denmark */
+    "de_DE",    /* German       Germany */
+    "din_SD",   /* Dinka        Sudan */
+    "doi_IN",   /* Dogri        India */
+    "dsb_DE",   /* Lower Sorbian        Germany */
+    "dv_MV",    /* Divehi       Maldives */
+    "dz_BT",    /* Dzongkha     Bhutan */
+    "ee_GH",    /* Éwé          Ghana */
+    "el_GR",    /* Greek        Greece */
+    /* Don't put "en_GB" or "en_US" here.  That would be asking for fruitless
+       political discussion.  */
+    "es_ES",    /* Spanish      Spain */
+    "et_EE",    /* Estonian     Estonia */
+    "fa_IR",    /* Persian      Iran */
+    "fi_FI",    /* Finnish      Finland */
+    "fil_PH",   /* Filipino     Philippines */
+    "fj_FJ",    /* Fijian       Fiji */
+    "fo_FO",    /* Faroese      Faeroe Islands */
+    "fon_BJ",   /* Fon          Benin */
+    "fr_FR",    /* French       France */
+    "fur_IT",   /* Friulian     Italy */
+    "fy_NL",    /* Western Frisian      Netherlands */
+    "ga_IE",    /* Irish        Ireland */
+    "gd_GB",    /* Scottish Gaelic      Britain */
+    "gon_IN",   /* Gondi        India */
+    "gsw_CH",   /* Swiss German Switzerland */
+    "gu_IN",    /* Gujarati     India */
+    "he_IL",    /* Hebrew       Israel */
+    "hi_IN",    /* Hindi        India */
+    "hil_PH",   /* Hiligaynon   Philippines */
+    "hr_HR",    /* Croatian     Croatia */
+    "hsb_DE",   /* Upper Sorbian        Germany */
+    "ht_HT",    /* Haitian      Haiti */
+    "hu_HU",    /* Hungarian    Hungary */
+    "hy_AM",    /* Armenian     Armenia */
+    "id_ID",    /* Indonesian   Indonesia */
+    "ig_NG",    /* Igbo         Nigeria */
+    "ii_CN",    /* Sichuan Yi   China */
+    "ilo_PH",   /* Iloko        Philippines */
+    "is_IS",    /* Icelandic    Iceland */
+    "it_IT",    /* Italian      Italy */
+    "ja_JP",    /* Japanese     Japan */
+    "jab_NG",   /* Hyam         Nigeria */
+    "jv_ID",    /* Javanese     Indonesia */
+    "ka_GE",    /* Georgian     Georgia */
+    "kab_DZ",   /* Kabyle       Algeria */
+    "kaj_NG",   /* Jju          Nigeria */
+    "kam_KE",   /* Kamba        Kenya */
+    "kmb_AO",   /* Kimbundu     Angola */
+    "kcg_NG",   /* Tyap         Nigeria */
+    "kdm_NG",   /* Kagoma       Nigeria */
+    "kg_CD",    /* Kongo        Democratic Republic of Congo */
+    "kk_KZ",    /* Kazakh       Kazakhstan */
+    "kl_GL",    /* Kalaallisut  Greenland */
+    "km_KH",    /* Central Khmer        Cambodia */
+    "kn_IN",    /* Kannada      India */
+    "ko_KR",    /* Korean       Korea (South) */
+    "kok_IN",   /* Konkani      India */
+    "kr_NG",    /* Kanuri       Nigeria */
+    "kru_IN",   /* Kurukh       India */
+    "ky_KG",    /* Kyrgyz       Kyrgyzstan */
+    "lg_UG",    /* Ganda        Uganda */
+    "li_BE",    /* Limburgish   Belgium */
+    "lo_LA",    /* Laotian      Laos */
+    "lt_LT",    /* Lithuanian   Lithuania */
+    "lu_CD",    /* Luba-Katanga Democratic Republic of Congo */
+    "lua_CD",   /* Luba-Lulua   Democratic Republic of Congo */
+    "luo_KE",   /* Luo          Kenya */
+    "lv_LV",    /* Latvian      Latvia */
+    "mad_ID",   /* Madurese     Indonesia */
+    "mag_IN",   /* Magahi       India */
+    "mai_IN",   /* Maithili     India */
+    "mak_ID",   /* Makasar      Indonesia */
+    "man_ML",   /* Mandingo     Mali */
+    "men_SL",   /* Mende        Sierra Leone */
+    "mfe_MU",   /* Mauritian Creole     Mauritius */
+    "mg_MG",    /* Malagasy     Madagascar */
+    "mi_NZ",    /* Maori        New Zealand */
+    "min_ID",   /* Minangkabau  Indonesia */
+    "mk_MK",    /* Macedonian   North Macedonia */
+    "ml_IN",    /* Malayalam    India */
+    "mn_MN",    /* Mongolian    Mongolia */
+    "mni_IN",   /* Manipuri     India */
+    "mos_BF",   /* Mossi        Burkina Faso */
+    "mr_IN",    /* Marathi      India */
+    "ms_MY",    /* Malay        Malaysia */
+    "mt_MT",    /* Maltese      Malta */
+    "mwr_IN",   /* Marwari      India */
+    "my_MM",    /* Burmese      Myanmar */
+    "na_NR",    /* Nauru        Nauru */
+    "nah_MX",   /* Nahuatl      Mexico */
+    "nap_IT",   /* Neapolitan   Italy */
+    "nb_NO",    /* Norwegian Bokmål    Norway */
+    "nds_DE",   /* Low Saxon    Germany */
+    "ne_NP",    /* Nepali       Nepal */
+    "nl_NL",    /* Dutch        Netherlands */
+    "nn_NO",    /* Norwegian Nynorsk    Norway */
+    "no_NO",    /* Norwegian    Norway */
+    "nr_ZA",    /* South Ndebele        South Africa */
+    "nso_ZA",   /* Northern Sotho       South Africa */
+    "ny_MW",    /* Chichewa     Malawi */
+    "nym_TZ",   /* Nyamwezi     Tanzania */
+    "nyn_UG",   /* Nyankole     Uganda */
+    "oc_FR",    /* Occitan      France */
+    "oj_CA",    /* Ojibwa       Canada */
+    "or_IN",    /* Oriya        India */
+    "pa_IN",    /* Punjabi      India */
+    "pag_PH",   /* Pangasinan   Philippines */
+    "pam_PH",   /* Pampanga     Philippines */
+    "pap_AN",   /* Papiamento   Netherlands Antilles - this line can be 
removed in 2018 */
+    "pbb_CO",   /* Páez         Colombia */
+    "pl_PL",    /* Polish       Poland */
+    "ps_AF",    /* Pashto       Afghanistan */
+    "pt_PT",    /* Portuguese   Portugal */
+    "raj_IN",   /* Rajasthani   India */
+    "rm_CH",    /* Romansh      Switzerland */
+    "rn_BI",    /* Kirundi      Burundi */
+    "ro_RO",    /* Romanian     Romania */
+    "ru_RU",    /* Russian      Russia */
+    "rw_RW",    /* Kinyarwanda  Rwanda */
+    "sa_IN",    /* Sanskrit     India */
+    "sah_RU",   /* Yakut        Russia */
+    "sas_ID",   /* Sasak        Indonesia */
+    "sat_IN",   /* Santali      India */
+    "sc_IT",    /* Sardinian    Italy */
+    "scn_IT",   /* Sicilian     Italy */
+    "sg_CF",    /* Sango        Central African Republic */
+    "shn_MM",   /* Shan         Myanmar */
+    "si_LK",    /* Sinhala      Sri Lanka */
+    "sid_ET",   /* Sidamo       Ethiopia */
+    "sk_SK",    /* Slovak       Slovakia */
+    "sl_SI",    /* Slovenian    Slovenia */
+    "sm_WS",    /* Samoan       Samoa */
+    "smn_FI",   /* Inari Sami   Finland */
+    "sms_FI",   /* Skolt Sami   Finland */
+    "so_SO",    /* Somali       Somalia */
+    "sq_AL",    /* Albanian     Albania */
+    "sr_RS",    /* Serbian      Serbia */
+    "srr_SN",   /* Serer        Senegal */
+    "suk_TZ",   /* Sukuma       Tanzania */
+    "sus_GN",   /* Susu         Guinea */
+    "sv_SE",    /* Swedish      Sweden */
+    "te_IN",    /* Telugu       India */
+    "tem_SL",   /* Timne        Sierra Leone */
+    "tet_ID",   /* Tetum        Indonesia */
+    "tg_TJ",    /* Tajik        Tajikistan */
+    "th_TH",    /* Thai         Thailand */
+    "ti_ER",    /* Tigrinya     Eritrea */
+    "tiv_NG",   /* Tiv          Nigeria */
+    "tk_TM",    /* Turkmen      Turkmenistan */
+    "tl_PH",    /* Tagalog      Philippines */
+    "to_TO",    /* Tonga        Tonga */
+    "tpi_PG",   /* Tok Pisin    Papua New Guinea */
+    "tr_TR",    /* Turkish      Turkey */
+    "tum_MW",   /* Tumbuka      Malawi */
+    "ug_CN",    /* Uighur       China */
+    "uk_UA",    /* Ukrainian    Ukraine */
+    "umb_AO",   /* Umbundu      Angola */
+    "ur_PK",    /* Urdu         Pakistan */
+    "uz_UZ",    /* Uzbek        Uzbekistan */
+    "ve_ZA",    /* Venda        South Africa */
+    "vi_VN",    /* Vietnamese   Vietnam */
+    "wa_BE",    /* Walloon      Belgium */
+    "wal_ET",   /* Walamo       Ethiopia */
+    "war_PH",   /* Waray        Philippines */
+    "wen_DE",   /* Sorbian      Germany */
+    "yao_MW",   /* Yao          Malawi */
+    "zap_MX"    /* Zapotec      Mexico */
+  };
+
+/* Compare just the language part of two locale names.  */
+static int
+langcmp (const char *locale1, const char *locale2)
+{
+  size_t locale1_len;
+  size_t locale2_len;
+  int cmp;
+
+  {
+    const char *locale1_end = strchr (locale1, '_');
+    if (locale1_end != NULL)
+      locale1_len = locale1_end - locale1;
+    else
+      locale1_len = strlen (locale1);
+  }
+  {
+    const char *locale2_end = strchr (locale2, '_');
+    if (locale2_end != NULL)
+      locale2_len = locale2_end - locale2;
+    else
+      locale2_len = strlen (locale2);
+  }
+
+  if (locale1_len < locale2_len)
+    {
+      cmp = memcmp (locale1, locale2, locale1_len);
+      if (cmp == 0)
+        cmp = -1;
+    }
+  else
+    {
+      cmp = memcmp (locale1, locale2, locale2_len);
+      if (locale1_len > locale2_len && cmp == 0)
+        cmp = 1;
+    }
+
+  return cmp;
+}
+
+/* Given a locale name, return the main locale with the same language,
+   or NULL if not found.
+   For example: "fr_DE" -> "fr_FR".  */
+static const char *
+get_main_locale_with_same_language (const char *locale)
+{
+#  define table locales_with_principal_territory
+  /* The table is sorted.  Perform a binary search.  */
+  size_t hi = sizeof (table) / sizeof (table[0]);
+  size_t lo = 0;
+  while (lo < hi)
+    {
+      /* Invariant:
+         for i < lo, langcmp (table[i], locale) < 0,
+         for i >= hi, langcmp (table[i], locale) > 0.  */
+      size_t mid = (hi + lo) >> 1; /* >= lo, < hi */
+      int cmp = langcmp (table[mid], locale);
+      if (cmp < 0)
+        lo = mid + 1;
+      else if (cmp > 0)
+        hi = mid;
+      else
+        {
+          /* Found an i with
+               langcmp (language_table[i], locale) == 0.
+             Verify that it is the only such i.  */
+          if (mid > lo && langcmp (table[mid - 1], locale) >= 0)
+            abort ();
+          if (mid + 1 < hi && langcmp (table[mid + 1], locale) <= 0)
+            abort ();
+          return table[mid];
+        }
+    }
+#  undef table
+  return NULL;
+}
+
+/* Mapping from territory to main language that is spoken in that territory.  
*/
+static char const locales_with_principal_language[][6 + 1] =
+  {
+    /* This is based on the set of existing locales in glibc, with duplicates
+       removed, and on the Wikipedia pages named "Languages of <territory>".
+       If in doubt, use the locale that exists in macOS.  For example, the only
+       "*_IN" locale in macOS 10.13 is "hi_IN", so use that.  */
+    /* A useful shell function for producing a line of this table is:
+         func_line ()
+         {
+           # Usage: func_line ll_CC
+           ll=`echo "$1" | sed -e 's|_.*||'`
+           cc=`echo "$1" | sed -e 's|^.*_||'`
+           llx=`sed -n -e "s|^${ll} ||p" < gettext-tools/doc/ISO_639`
+           ccx=`expand gettext-tools/doc/ISO_3166 | sed -n -e "s|^${cc}  *||p"`
+           echo "    \"$1\",    /$X* ${llx} ${ccx} *$X/"
+         }
+     */
+              /* Main language  Territory */
+    "ca_AD",    /* Catalan      Andorra */
+    "ar_AE",    /* Arabic       United Arab Emirates */
+    "ps_AF",    /* Pashto       Afghanistan */
+    "en_AG",    /* English      Antigua and Barbuda */
+    "sq_AL",    /* Albanian     Albania */
+    "hy_AM",    /* Armenian     Armenia */
+    "pap_AN",   /* Papiamento   Netherlands Antilles - this line can be 
removed in 2018 */
+    "pt_AO",    /* Portuguese   Angola */
+    "es_AR",    /* Spanish      Argentina */
+    "de_AT",    /* German       Austria */
+    "en_AU",    /* English      Australia */
+    /* Aruba has two official languages: "nl_AW", "pap_AW".  */
+    "az_AZ",    /* Azerbaijani  Azerbaijan */
+    "bs_BA",    /* Bosnian      Bosnia */
+    "bn_BD",    /* Bengali      Bangladesh */
+    "nl_BE",    /* Dutch        Belgium */
+    "fr_BF",    /* French       Burkina Faso */
+    "bg_BG",    /* Bulgarian    Bulgaria */
+    "ar_BH",    /* Arabic       Bahrain */
+    "rn_BI",    /* Kirundi      Burundi */
+    "fr_BJ",    /* French       Benin */
+    "es_BO",    /* Spanish      Bolivia */
+    "pt_BR",    /* Portuguese   Brazil */
+    "dz_BT",    /* Dzongkha     Bhutan */
+    "en_BW",    /* English      Botswana */
+    "be_BY",    /* Belarusian   Belarus */
+    "en_CA",    /* English      Canada */
+    "fr_CD",    /* French       Democratic Republic of Congo */
+    "sg_CF",    /* Sango        Central African Republic */
+    "de_CH",    /* German       Switzerland */
+    "es_CL",    /* Spanish      Chile */
+    "zh_CN",    /* Chinese      China */
+    "es_CO",    /* Spanish      Colombia */
+    "es_CR",    /* Spanish      Costa Rica */
+    "es_CU",    /* Spanish      Cuba */
+    /* Curaçao has three official languages: "nl_CW", "pap_CW", "en_CW".  */
+    "el_CY",    /* Greek        Cyprus */
+    "cs_CZ",    /* Czech        Czech Republic */
+    "de_DE",    /* German       Germany */
+    /* Djibouti has two official languages: "ar_DJ" and "fr_DJ".  */
+    "da_DK",    /* Danish       Denmark */
+    "es_DO",    /* Spanish      Dominican Republic */
+    "ar_DZ",    /* Arabic       Algeria */
+    "es_EC",    /* Spanish      Ecuador */
+    "et_EE",    /* Estonian     Estonia */
+    "ar_EG",    /* Arabic       Egypt */
+    "ti_ER",    /* Tigrinya     Eritrea */
+    "es_ES",    /* Spanish      Spain */
+    "am_ET",    /* Amharic      Ethiopia */
+    "fi_FI",    /* Finnish      Finland */
+    /* Fiji has three official languages: "en_FJ", "fj_FJ", "hif_FJ".  */
+    "fo_FO",    /* Faroese      Faeroe Islands */
+    "fr_FR",    /* French       France */
+    "en_GB",    /* English      Britain */
+    "ka_GE",    /* Georgian     Georgia */
+    "en_GH",    /* English      Ghana */
+    "kl_GL",    /* Kalaallisut  Greenland */
+    "fr_GN",    /* French       Guinea */
+    "el_GR",    /* Greek        Greece */
+    "es_GT",    /* Spanish      Guatemala */
+    "zh_HK",    /* Chinese      Hong Kong */
+    "es_HN",    /* Spanish      Honduras */
+    "hr_HR",    /* Croatian     Croatia */
+    "ht_HT",    /* Haitian      Haiti */
+    "hu_HU",    /* Hungarian    Hungary */
+    "id_ID",    /* Indonesian   Indonesia */
+    "en_IE",    /* English      Ireland */
+    "he_IL",    /* Hebrew       Israel */
+    "hi_IN",    /* Hindi        India */
+    "ar_IQ",    /* Arabic       Iraq */
+    "fa_IR",    /* Persian      Iran */
+    "is_IS",    /* Icelandic    Iceland */
+    "it_IT",    /* Italian      Italy */
+    "ar_JO",    /* Arabic       Jordan */
+    "ja_JP",    /* Japanese     Japan */
+    "sw_KE",    /* Swahili      Kenya */
+    "ky_KG",    /* Kyrgyz       Kyrgyzstan */
+    "km_KH",    /* Central Khmer        Cambodia */
+    "ko_KR",    /* Korean       Korea (South) */
+    "ar_KW",    /* Arabic       Kuwait */
+    "kk_KZ",    /* Kazakh       Kazakhstan */
+    "lo_LA",    /* Laotian      Laos */
+    "ar_LB",    /* Arabic       Lebanon */
+    "de_LI",    /* German       Liechtenstein */
+    "si_LK",    /* Sinhala      Sri Lanka */
+    "lt_LT",    /* Lithuanian   Lithuania */
+    /* Luxembourg has three official languages: "lb_LU", "fr_LU", "de_LU".  */
+    "lv_LV",    /* Latvian      Latvia */
+    "ar_LY",    /* Arabic       Libya */
+    "ar_MA",    /* Arabic       Morocco */
+    "sr_ME",    /* Serbian      Montenegro */
+    "mg_MG",    /* Malagasy     Madagascar */
+    "mk_MK",    /* Macedonian   North Macedonia */
+    "fr_ML",    /* French       Mali */
+    "my_MM",    /* Burmese      Myanmar */
+    "mn_MN",    /* Mongolian    Mongolia */
+    "mt_MT",    /* Maltese      Malta */
+    "mfe_MU",   /* Mauritian Creole     Mauritius */
+    "dv_MV",    /* Divehi       Maldives */
+    "ny_MW",    /* Chichewa     Malawi */
+    "es_MX",    /* Spanish      Mexico */
+    "ms_MY",    /* Malay        Malaysia */
+    "en_NG",    /* English      Nigeria */
+    "es_NI",    /* Spanish      Nicaragua */
+    "nl_NL",    /* Dutch        Netherlands */
+    "no_NO",    /* Norwegian    Norway */
+    "ne_NP",    /* Nepali       Nepal */
+    "na_NR",    /* Nauru        Nauru */
+    "niu_NU",   /* Niuean       Niue */
+    "en_NZ",    /* English      New Zealand */
+    "ar_OM",    /* Arabic       Oman */
+    "es_PA",    /* Spanish      Panama */
+    "es_PE",    /* Spanish      Peru */
+    "tpi_PG",   /* Tok Pisin    Papua New Guinea */
+    "fil_PH",   /* Filipino     Philippines */
+    "pa_PK",    /* Punjabi      Pakistan */
+    "pl_PL",    /* Polish       Poland */
+    "es_PR",    /* Spanish      Puerto Rico */
+    "pt_PT",    /* Portuguese   Portugal */
+    "es_PY",    /* Spanish      Paraguay */
+    "ar_QA",    /* Arabic       Qatar */
+    "ro_RO",    /* Romanian     Romania */
+    "sr_RS",    /* Serbian      Serbia */
+    "ru_RU",    /* Russian      Russia */
+    "rw_RW",    /* Kinyarwanda  Rwanda */
+    "ar_SA",    /* Arabic       Saudi Arabia */
+    "en_SC",    /* English      Seychelles */
+    "ar_SD",    /* Arabic       Sudan */
+    "sv_SE",    /* Swedish      Sweden */
+    "en_SG",    /* English      Singapore */
+    "sl_SI",    /* Slovenian    Slovenia */
+    "sk_SK",    /* Slovak       Slovakia */
+    "en_SL",    /* English      Sierra Leone */
+    "fr_SN",    /* French       Senegal */
+    "so_SO",    /* Somali       Somalia */
+    "ar_SS",    /* Arabic       South Sudan */
+    "es_SV",    /* Spanish      El Salvador */
+    "ar_SY",    /* Arabic       Syria */
+    "th_TH",    /* Thai         Thailand */
+    "tg_TJ",    /* Tajik        Tajikistan */
+    "tk_TM",    /* Turkmen      Turkmenistan */
+    "ar_TN",    /* Arabic       Tunisia */
+    "to_TO",    /* Tonga        Tonga */
+    "tr_TR",    /* Turkish      Turkey */
+    "zh_TW",    /* Chinese      Taiwan */
+    "sw_TZ",    /* Swahili      Tanzania */
+    "uk_UA",    /* Ukrainian    Ukraine */
+    "lg_UG",    /* Ganda        Uganda */
+    "en_US",    /* English      United States of America */
+    "es_UY",    /* Spanish      Uruguay */
+    "uz_UZ",    /* Uzbek        Uzbekistan */
+    "es_VE",    /* Spanish      Venezuela */
+    "vi_VN",    /* Vietnamese   Vietnam */
+    "bi_VU",    /* Bislama      Vanuatu */
+    "sm_WS",    /* Samoan       Samoa */
+    "ar_YE",    /* Arabic       Yemen */
+    "en_ZA",    /* English      South Africa */
+    "en_ZM",    /* English      Zambia */
+    "en_ZW"     /* English      Zimbabwe */
+  };
+
+/* Compare just the territory part of two locale names.  */
+static int
+terrcmp (const char *locale1, const char *locale2)
+{
+  const char *territory1 = strrchr (locale1, '_') + 1;
+  const char *territory2 = strrchr (locale2, '_') + 1;
+
+  return strcmp (territory1, territory2);
+}
+
+/* Given a locale name, return the locale corresponding to the main language
+   with the same territory, or NULL if not found.
+   For example: "fr_DE" -> "de_DE".  */
+static const char *
+get_main_locale_with_same_territory (const char *locale)
+{
+  if (strrchr (locale, '_') != NULL)
+    {
+#  define table locales_with_principal_language
+      /* The table is sorted.  Perform a binary search.  */
+      size_t hi = sizeof (table) / sizeof (table[0]);
+      size_t lo = 0;
+      while (lo < hi)
+        {
+          /* Invariant:
+             for i < lo, terrcmp (table[i], locale) < 0,
+             for i >= hi, terrcmp (table[i], locale) > 0.  */
+          size_t mid = (hi + lo) >> 1; /* >= lo, < hi */
+          int cmp = terrcmp (table[mid], locale);
+          if (cmp < 0)
+            lo = mid + 1;
+          else if (cmp > 0)
+            hi = mid;
+          else
+            {
+              /* Found an i with
+                   terrcmp (language_table[i], locale) == 0.
+                 Verify that it is the only such i.  */
+              if (mid > lo && terrcmp (table[mid - 1], locale) >= 0)
+                abort ();
+              if (mid + 1 < hi && terrcmp (table[mid + 1], locale) <= 0)
+                abort ();
+              return table[mid];
+            }
+        }
+#  undef table
+    }
+  return NULL;
+}
+
+# endif
+
 char *
 rpl_setlocale (int category, const char *locale)
 {
@@ -941,16 +1462,18 @@ rpl_setlocale (int category, const char *locale)
                     /* On Mac OS X 10.13, some locales can be set through
                        System Preferences > Language & Region, that are not
                        supported by libc.  The system's setlocale() falls
-                       back to "C" for these locale categories.  We can 
possibly
-                       do better.  If we can't, print a warning, to limit user
+                       back to "C" for these locale categories.  We can do
+                       better, by trying an existing locale with the same
+                       language or an existing locale with the same territory.
+                       If we can't, print a warning, to limit user
                        expectations.  */
-                    int warn = 1;
+                    int warn = 0;
 
                     if (cat == LC_CTYPE)
                       warn = (setlocale_single (cat, "UTF-8") == NULL);
-#  if HAVE_CFLOCALECOPYPREFERREDLANGUAGES || HAVE_CFPREFERENCESCOPYAPPVALUE /* 
MacOS X 10.4 or newer */
                     else if (cat == LC_MESSAGES)
                       {
+#  if HAVE_CFLOCALECOPYPREFERREDLANGUAGES || HAVE_CFPREFERENCESCOPYAPPVALUE /* 
MacOS X 10.4 or newer */
                         /* Take the primary language preference.  */
 #   if HAVE_CFLOCALECOPYPREFERREDLANGUAGES /* MacOS X 10.5 or newer */
                         CFArrayRef prefArray = CFLocaleCopyPreferredLanguages 
();
@@ -985,7 +1508,15 @@ rpl_setlocale (int category, const char *locale)
                                     gl_locale_name_canonicalize (buf);
 
                                     /* Try setlocale with this value.  */
-                                    warn = (setlocale_single (cat, buf) == 
NULL);
+                                    if (setlocale_single (cat, buf) == NULL)
+                                      {
+                                        const char *last_try =
+                                          get_main_locale_with_same_language 
(buf);
+
+                                        if (last_try == NULL
+                                            || setlocale_single (cat, 
last_try) == NULL)
+                                          warn = 1;
+                                      }
                                   }
                               }
 #   if HAVE_CFLOCALECOPYPREFERREDLANGUAGES /* MacOS X 10.5 or newer */
@@ -993,24 +1524,51 @@ rpl_setlocale (int category, const char *locale)
 #   elif HAVE_CFPREFERENCESCOPYAPPVALUE /* MacOS X 10.4 or newer */
                           }
 #   endif
-                      }
+#  else
+                        const char *last_try =
+                          get_main_locale_with_same_language (name);
+
+                        if (last_try == NULL
+                            || setlocale_single (cat, last_try) == NULL)
+                          warn = 1;
 #  endif
-                    /* No fallback possible for LC_NUMERIC.  The application
-                       should use the locale properties
-                       kCFLocaleDecimalSeparator, kCFLocaleGroupingSeparator.
-                       No fallback possible for LC_TIME.  The application 
should
-                       use the locale property kCFLocaleCalendarIdentifier.
-                       No fallback possible for LC_COLLATE.  The application
-                       should use the locale properties
-                       kCFLocaleCollationIdentifier, 
kCFLocaleCollatorIdentifier.
-                       No fallback possible for LC_MONETARY.  The application
-                       should use the locale properties
-                       kCFLocaleCurrencySymbol, kCFLocaleCurrencyCode.  */
+                      }
+                    else
+                      {
+                        /* For LC_NUMERIC, the application should use the 
locale
+                           properties kCFLocaleDecimalSeparator,
+                           kCFLocaleGroupingSeparator.
+                           For LC_TIME, the application should use the locale
+                           property kCFLocaleCalendarIdentifier.
+                           For LC_COLLATE, the application should use the 
locale
+                           properties kCFLocaleCollationIdentifier,
+                           kCFLocaleCollatorIdentifier.
+                           For LC_MONETARY, the applicationshould use the 
locale
+                           properties kCFLocaleCurrencySymbol,
+                           kCFLocaleCurrencyCode.
+                           But since most applications don't have macOS 
specific
+                           code like this, try an existing locale with the same
+                           territory.  */
+                        const char *last_try =
+                          get_main_locale_with_same_territory (name);
+
+                        if (last_try == NULL
+                            || setlocale_single (cat, last_try) == NULL)
+                          warn = 1;
+                      }
 
                     if (warn)
-                      fprintf (stderr,
-                               "Warning: Failed to set locale category %s to 
%s.\n",
-                               category_to_name (cat), name);
+                      {
+                        /* Warn only if the environment variable
+                           SETLOCALE_VERBOSE is set.  Otherwise these warnings
+                           are just annoyances, since normal users won't invoke
+                           'localedef'.  */
+                        const char *verbose = getenv ("SETLOCALE_VERBOSE");
+                        if (verbose != NULL && verbose[0] != '\0')
+                          fprintf (stderr,
+                                   "Warning: Failed to set locale category %s 
to %s.\n",
+                                   category_to_name (cat), name);
+                      }
                   }
 # else
                   goto fail;