"The truth is, I can speak English, but I'm translating."
However, this translation sounds a bit awkward in English. Here are some more natural ways to say it:
* "To be honest, I can speak English, but I'm translating."
* "Actually, I can speak English, but I'm translating."
* "I can speak English, but I'm translating this for you."
These options are more idiomatic and convey the same meaning in a clearer way.