If you use language inheritance (for example Italian and Swiss-Italian as inherited language) you can select both languages in the administration.

In order to use the inheritance you have to enter the Italian Translation first. It will inherit to Swiss-Italian.

If you ever (accidentally) save a translation for Swiss-Italian there is no way to revert to language inheritance for the record you saved. If you ever need to update the record you will always have to save it in Italian and in Swiss-Italian.

There should be a way to delete the translation and reactivate the inheritance