I've already posted this topic at Talk:Content translation/Machine Translation/Yandex. Because nobody answered, I'm re-posting it here that it can bee seen by more people.
Topic on Talk:Content translation
Why isn't Yandex.Translate enabled for English to German?
Install the script, shown previous topics in this talk, in each language projects in Your user namespace and You will be lucky.
Thanks for the feedback @FF-11.
Machine translation support is being enabled gradually on different languages. It is not available yet for translating into German or English, but getting feedback from users on those Wikipedia communities is very helpful for the next steps in expanding the language support. I've captured your request in this ticket.