After executing the following code
(easy-menu-define test-menu (current-local-map) "doc"
`("xxx"
(,(concat (string (decode-char 'ucs 915)) " \\Gamma"))
("G \\Gamma")))
in an Emacs compiled with support for GTK menus, there will be a new
"xxx" menu with two entries. I expected the first menu entry to show
an upper case gamma, a space and the string "\Gamma". But the space
and the backslash don't come out right. The characters look similar
to a "normal" space and backslash, but appear too wide. You should
see this by comparing the first menu entry with the second. The
latter shows a "normal" space and backslash.