git-tp-sync doesn't add new langs to LINGUAS

The git-tp-sync script doesn't add new translations' language code to the LINGUAS file. That's because it was created for util-linux, which doesn't have LINGUAS file. Since xdg-user-dirs has and use the LINGUAS file, this script has to be adapted; otherwise, translation files will be added to the source code, but not included in the build and installation process.