Guys, here is an explanation why you don't see your WP instance in the selected language
WordPress sends the translations to the WP websites when they are at least 95% translated. AcyMailing is, for example, translated in "German (Formal)", but has only 11% for the "German" language, this is why it isn't translated on any site using German language website.
There are 2560 translated lines for the German language that are waiting for official WP translation managers to be approved. The way WordPress handles the translation ensures good quality translation but it takes ages to be applied :/
For the French language for example we managed to make it work after 5 months even though we are French people 😅
As you can see, this language translation and approval process is all out of our scope, and we all depend on the official translation team to approve something
