I also work in a non-English speaking environment. I typically respond in English (and will ask, "can you say that in English?") or need to ask them to translate documents they've sent me, and everyone's really nice about it. Hopefully they will be in your workplace too. I've enrolled in an evening language class starting in August to increase my confidence in speaking - not sure if that would help you too but figured I'd share how I'm tackling the language barrier.