From your other post enquiring about starting a forum in English language and asking about subjects Poles would be interested in, it seems as if you don't really know much about Poland and Poles to be honest. If your website is to be exclusively for Poles, why would you need English language anyway?
Whether it's a good idea or not, you don't appear to have put much thought into this so far.
Running a forum will take up more of your time than you probably think, and unless you have Polish friends to help you for example, how are you going to moderate it and understand what is being discussed when you don't speak Polish?
