There were definitely some words in there which I had never heard even as a native English speaker. One suggestion I would make if the intent is to teach people a new language would be to limit the word list based on how commonly used the words are. I don't think it helps non-proficient speakers to learn extremely obscure words that nobody uses.
You could make it so that the X most common words are needed to win and the rest are bonus points or something.
1. I thought there were a few too many clues of various types. The emoji, combined with the word list in alphabetical order, the part-filled words, AND the infinite guesses. I'll admit, I ended up guessing quite a few times, which slightly soured the experience.
2. Some of the words are really weird. I'm not sure all of the onomatopoeic words should be in there. And I don't think the acronyms (e.g NNW) should be in there.
Other than that, though, I thought it was a great version of the NYT equivalent. Loved that there were so many words — it's a shame that #2 would mean fewer, but I still think it would be worth being a bit pickier on balance. My partner didn't quite get the emjoi clues until I explained an example, but I thought a lot of them were quite clever!
Some feedback on the UI - at least on desktop Chrome, the title part of your scoreboard area is being cut off and the "How to Play" section has the text totally flush with the top, so you might want to look into your margins or padding there to give everything some breathing room. There's also a bug in your shuffle algorithm -- the letter in the top right cell never changes when you shuffle the letters. The cell buttons are also a little unresponsive. It seems like there are some dead zones where the hover animation doesn't get triggered and clicking the cell doesn't actually input the letter.
I like how you've added some features to make it easier for language learners to find words. Are you yourself studying German? And if so have you found it fun/useful?
one thing.. 'ween' is a word.
Some of it was a little frustrating, mostly the acronyms. Labeling them as such might help, because I was going mad trying to figure out "NNW" and "WWOOF.". Also, performance was not great on my older Android phone - the app would sometimes miss letters that I was sure I'd clicked.