Hi,

Enable the developer mode.

Firstly, enable the required languages.

Then remove the 'de_CH' language from the users who used this language. For that go to users and changed the  language of the user.

Do the same for all users who use this language.

Then go to languages and disable the language 'de_CH'.

After disabling the language

Hope it helps.

Thanks. The field already was set to de_DE. I've also been digging through the menus and noticed that there was another "Language" field in "Private informations" of "my profile" but changing it to de_DE also didn't help.

Seems there's still something else hidden from my newbie eyes! Let's see if some sleep helps with finding it.

Check user if they have selected the new language and if so - change to de_DE and then try to uninstall the de_CH