i dont know ^_^

You describe a person's speech as fluent. Flowing gives a slightly different image (literally, of water or another real liquid). Be careful of confusing similar words like these! His English is fluent. Her speech is fluent. They speak English fluently.

I am sure that it would be correct to say "he has a smooth/flowing (as fluent as liquid) English"

When you have a flow, you speak fluently and naturally.