Today I knocked together a German language clone of Stacksmith's Spellbinder. I'm calling it Zaubuchstabier, even if I'm not sure how well that works as a pun.
The rules mostly go through unchanged, but I had to think what to do about conjugated endings. The solution I settled on is to only allow one word per stem -- if you try multiple words with the same stem, only the longest will count towards your score.
The wordlist consists of those words which have entries in german wiktionary and are also in the wordlist below. This obviously won't be as high quality as Stacksmith's hand-curated list, but may be good enough. The stemmer needs some work.
Have fun, let me know if there's anything wrong or missing or improvable.