I plan on asking my girlfriends parents for their blessing before I propose but the problem is her parents don''t speak English very well & I can not speak their language very well either.
Any advise on what I should do?
Do you know someone who can accompany you and translate? If you live near a university, there may be someone on the foreign language faculty who could help you or could recommend someone to you who could help you rehearse asking the question in her parent's native language.
Does she have any friends or other relatives that speak both languages that could go along? Don't forget another thing too. Language is one barrier, but culture is another. You don't just need a translator you need a cultural translator as well. Ask someone from her parents culture how a man would typically approach this situation. Do you bring a gift? What kind of gift? Do you speak only to the father, to both? Although cultural traditions vary widely even within cultures it can't hurt to have some background. You can probably research this on the Internet too. If you tell us the cultural background you're talking about we can help here too. I've even seen someone provide phonetic spellings of phrases that someone wanted to learn.