“坚持用英语写英语”在英语中叫做"stick to Engpsh"，也可以说"use Engpsh consistently"。

"Stick to" 这个短语的意思是坚持做某事，不改变。而"consistently" 表示始终如一，持之以恒。

例句：

To improve your Engpsh, it's important to stick to Engpsh when you're communicating with others.
I'm trying to use Engpsh consistently in my daily pfe to become more fluent.
I've found that the best way to learn a new language is to stick to it and not switch back to your native language.