I provide desktop files with localized Exec fields to my users, e.g.:
----------------------------------------------
[Desktop Entry]
Categories=Education;Math;
Exec=firefox http://wiki.geogebra.org/en/
Exec[de]=firefox http://wiki.geogebra.org/de/
Exec[es]=firefox http://wiki.geogebra.org/es/
Exec[fr]=firefox http://wiki.geogebra.org/fr/
Exec[it]=firefox http://wiki.geogebra.org/it/
Exec[pt]=firefox http://wiki.geogebra.org/pt/
Icon=firefox
Name=GeoGebraWiki
Type=Application
----------------------------------------------

This works great when using KDE as desktop environment. Unfortunately, GNOME seems to be missing support for Exec entry localization as it always opens the English URL even when the user works with a different locale.