Depends on where you are. If you say zhong wen in China, no problem. If you say zhong wen anywhere else in the world, people are probably going to get confused. The downside for han yu is people might think you are saying 'korean' if your tones aren't spot on.

"Wo hui shuo yidian han yu" is better.

Both okay... man, it's hard to read pinyin :P

I think these two sentences are the same, in my own opinion, “wo de zhong wen bu shi hen hao” is better.

Wo Hui shuo hanyu yi Dian