Beijing Language School, I think, is the best university to learn the Chinese language. Besides, it's located in the capital of China and you can enjoy the culture there. Actually, Nanjing University is also a good choice. I'm a undergraduate of Institute For International Students of this university, so I'm familiar with this school. Short programs during winter and summer break (about 2--10 weeks) are also available. If you come here, glad to be your friend.