I experience the same problem as was described at https://stackoverflow.com/questions/66444932/adding-more-languages-in-wikibase.
So, let's create an entity with a label, alias and description in default English language. Then I want to add label in German, for example. But the Wikibase frontend does not show labels, aliases and descriptions in non-English languages in editing mode. Well, I can I add the labels via API, but not via GUI.
Is it by purpose? I use the latest Wikibase Release Pipeline Docker.