my own Tests show that only a replace of the German Language with the English one works well. At first I tried to add the German Language to the Server which gave me similar results you described. The only point is that the replace don`t let you choose which Templates you want to change, but we a.e. always uses the English NAB template, you can save this before the procedure and copy it back manually after it.
Their is an issue relating to Adding Language Packs documented in the readme file that comes with the language packs.
If you want to have a multilingual templaet, you have to first erplace the language with the International English Language Pack. After that you can add othe languages.
I have French, German, Dutch, Norwegian, Swedish, Finnish and Danish all working perfectly. For some erason Spanish and Italian don’t seem to want to go past 40% when it is adding the languages to Bookmark.ntf.