You may not be suprised to hear it from me but I think the language is the most significant thing. If you want to have more Bulgarian friends you should know the language. Otherwise you will limit yourself only to people who can speak good English. Communication is the most important thing among good friends - sharing stories and thoughts, telling and listening to jokes (and you'll be able to understand the jokes only if you know the language), discussing movies and books, even sharing a common slang. And still you’re lucky because you can find people fluent in English to be friend with but imagine if your mother tongue was not so common. When we (Bulgarians) live abroad we don’t expect anyone to speak to us in our own language and thus make things easier for us. If we want to have friends we have to speak the language of the country we live in. So when hanging out with your Bulgarian friends ask them to speak to you in Bulgarian so you’ll be able to learn phrases and words the easiest way. But I should also say that your Bulgarian is already very good, you just have to be more self-confident and break this language barrier. I know this is the hardest thing especially for people like you (and me) who have a linguistic and literature education because we know exactly how wrong we sound sometimes and we care a lot – this is our professional deformation :)