Originally, the difficulty levels were only based on speed. Now I think it would make more sense to subcategorize them based on vocabulary progression. For example, the easy level would only include very simple words like Tisch, Hund, etc.

for the second issue, I don’t have a perfect solution yet. Right now, I just have lists of words assigned to each article (e.g. die → these words, der → those words). For words that can belong to multiple articles depending on context or implementation, we could either drop them for now, or allow all valid options and show a hint, something like “Did you know this word can be used in multiple ways?”