Identify your weaknesses. What are they? Language? Specifically? Grammar, vocabulary? Or higher-level communication? Or interviews, specifically?
I'm twice non-native speaker (English, German) but got good enough to do communication-focused roles without big problems.
From my point of view, language requires training in grammar and a satisfactory vocabulary.
Grammar most probably really need training (like language courses), I think it's quite hard to get all these tenses and modal verbs etc. right.
For vocabulary check Duolingo, good for training.
Read a lot in the language, listen a lot to the speech.
A couple of friends who learn eastern-European languages book private lessons over Skype, you can get a professional tutor quite cheap. Not sure if this will work for English, though.
Consider spending several month abroad (some Work&Travel programm). Full integration is the best way to learn the language.
As for interviews, read a few books on interviews (like "Programming Interviews Exposed") and do a lot of interviews. Go to interviews just for training. It's just a matter of practice. After a dozen of interviews you'll know the show.