it's like you know English as well as your first language.

看起来你对英语的了解就像你的母语一样了。

It's like 课堂 - SpeakingMax英语口语达人

Most Jews in the first century would've used Greek as their first language,not Hebrew or even Aramaic.

主后第一世纪大多数犹太人都把希腊语当作第一语言,而不是希伯来语或阿拉米语。

耶鲁公开课 - 新约课程节选

The French essayist Michel de Montaigne was brought up speaking Latin as his first language and as a boy read Ovid's Metamorphoses for fun.

BBC: Pope resignation: Who speaks Latin these days?

Neither party speaks English as their first language - idioms can easily be misunderstood.

BBC: Imagine the meeting that led to The Shard

Cornish is believed to have died out as a first language in the late 18th Century.

BBC: Land's End Cornish translation removal criticised