Blog in English.
Job-wise it will demonstrate your ability to communicate to the largest audience possible and consume from the largest source of information and knowledge available.
I've also been blogging in English which is not my native language. I find it's better to make my writings accessible to everyone without building barriers. It may also sound funny but I express my programming-related thoughts in English much better than in any other language - I've learned hugely from English books and documentation and I've adopted their terminology. I'd be striving hard now to translate many concepts and ideas even into my native language.
Anyway I somehow feel if the folks are unable to read an English blog, they're probably not in a good position to appreciate the content even if it were in their native language, for the simple reason their language barrier has likely kept them in isolation from the ideas and happenings filling the programming air.
Ah yes, and something very important forgotten - writing in English will help you bring up your English skills.