Generally Japanese posters enjoy knowing they have fans overseas! And it's better to type what you intend than attempt to type in a language you cannot speak. It doesn't look rude at all though~
I would be a little careful of words with opposite meanings though or idioms. Like "that song is sick" or "that's tight". Be direct with your post so the auto translator can pick it up properly.
Got sick of seeing the same anger farming shit every day, then found out about the luigi censorship and just left. Honestly best choice. I'm enjoying lemmy so far, and the control I have over my experience.