Currently it seems not possible to have working gettext translations without included a patched glibc build in your snap - the core image doesn't have locales definition that can be worked around by including locales definitions in the snap, though that's tedious, ideally snapcraft would help there - traditional desktop applications are built with calls to 'bindtextdomain ("domain", LOCALEDIR)', where LOCALDIR is defined at buildtime and so pointing to /usr there seems to be no way to redirect to another directory at runtime - desktop applications needs system library translations sometime which means langpacks need to be included in snaps