I think when you believe that a language is beautiful is like when you believe that something is art, you can try to understand why is beautiful, and you can put parameters but at the end there isn't a criterion, just you like it. In this sense I like German for its stucture and its logic, English for its simplicity, French for its sounds. But I think Catalan is my favorite, and I don't know why, just I like it. 

I like how Russian sounds.

The most beautuful language is one that express feelings and we all understand.

There are two languages that can do that:

Music is the first one.

Do you guess what the second one is? ^_^

I think English is the most beautiful language because of the sound.

For me, Mandarin seems to be the most beautiful language because I like the way it is written.