Well, I do "know" English well enough, and PL - ENG translation forms at least 50% of the work I do ;-p
Translating into a second language is about 10 times harder than translating into your own as there's almost no way to become fluent enough in a foreign language to develop a sense of style and euphony that can match that of native speakers. Typically translation into a second language, even when grammatically okay can sound heavy and/or dull or just stylistically off. I used to do proofing for a translation office's Polish to English work and 90 % of the changes I made were related to style (or fine grained vocabulary or set expressions the translator didn't know).
Unfortunately there aren't enough English speakers who are competent enough in Polish to meet demand and there's no sign that the situation will improve. There's EU money for schools to help train Polish to English translators but not much interest on the Polish side.
Back on topic, I will say that I sometimes do the opposite and import Polish words into English (when I think the other person will understand)
"I put it in the szafa."
"She as in the stolowka the last I saw her."
"I need to renew my zameldowanie."
"Is she still marudzic-ing?" (yes I heard myself say that recently)
I also sometimes add Polish diminutives to words.
"Do you want some wine-ik?"
etc etc etc