Why can’t I select alternative Working Languages in Term Store Management Tool?

I tried to create a multi-lingual term sets for a SharePoint Online Team Site following this guide. When trying to change the working language all options are grayed out and I can’t select them. Same goes for the other locales option. Under Site Settings > Language Settings the default language is English and all Alternative Languages are enabled. What do I have to do, to add another working language?

Any help would be greatly appreciated, Thanks

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