Don't speak for your friend; speak for yourself.

不要再为人说项了，谈谈你自己的看法吧。

Hey, speak for yourself here.

说你自己吧，别捎上我。

Let your work speak for yourself.

让你的作品为你发声。

Speak for yourself.

代表你自己说话。

Speak for yourself. I think I played quite well.

你只能说你自己，我觉得我表现得很不错。