I have Ubuntu on my desktop and I got the same issue. I couldn't be bothered to figure it out though so I play on my laptop now. But the ? and textures are definitely cause of Ubuntu. I think it (the ?) has to do with some language pack? I don't quite know as the last time I took a swing at that issue was close to a year ago. Hopefully someone else has some insight as to how to fix your issue.Here's a guide that was posted a while back. Don't know if its complete or not though.