Adding a translation in the new build system

[Pantxo Diribarne]

Hi,

I am trying to add a new translation (eu_ES.ts, see [1]) file in the 
default branch build system and out of source compilation ends up with 
this error:

...
  GEN      libgui/languages/be_BY.qm
  GEN      libgui/languages/de_DE.qm
  GEN      libgui/languages/en_US.qm
make[2]: *** Pas de règle pour fabriquer la cible « 
libgui/languages/eu_ES.qm », nécessaire pour « all-am ». Arrêt.

 ...

This is the french sentence for classical "no rule to make target ..."
I modified libgui/module.mk to include the eu_ES.ts file but it doesn't 
seam to be enough. What did I miss?
Note that I started with a clean (empty) build directory so that no 
cruft is left-over from previous builds.

Pantxo

[1] https://savannah.gnu.org/bugs/index.php?46041