Is it allowed to create riddles containing partly languages which are not english? If yes, which languages are allowed?
If you want to post a puzzle written in a specific language, then sorry you can't (according to this policy). But if you want to post a puzzle which needs the knowledge of any specific language, please feel free.
language tag should only be used in case when the answerer needs to know about a foreign language while answering, not while reading the puzzle.
Have a look at this meta post too.
There is the tag japanese for puzzles that use Japanese characters or the Japanese language. You may want to check out the corresponding puzzles, and compare the puzzle-type to your puzzle.