I had a similar problem, in my experience is a skill that can be acquired rather quickly. I had nice results with SQR3 reading method, roughly like this:
- Skim the material, get the basic idea
- Think of several questions you have for this material, given it's basic idea
- Read it again, slowly and thoroughly
- Go back to your questions and write down answers for them
Gradually this can get your more comfortable expressing things in your own language.