I can't speak English fluently as I am out of practice.

我不能流利地说英语，因为我已荒疏了。

《新英汉大辞典》

In order to speak English fluently, you need to think in English.

为了说一口流利的英语，你需要用英语思考。

youdao

She speaks English fluently.

她英语讲得很流利。

youdao

Four out of five second-generation immigrant children speak English fluently, but the same proportion are also fluent in Spanish.

BBC: Life in Spanglish for California's young Latinos

But today their job prospects are rosier - they are well equipped for multinational customer service positions and speak English fluently.

BBC: Anglo-Indians: Is their culture dying out?

Then again, if English brings wealth why is Africa still downtrodden despite many Africans speaking English more fluently than the Japanese?

FORBES: English - The Language of Global Business?