My native language is Serbian, but from my early age I started to learn English. And now, when I am a programmer I read almost all stuff in English (stuff for college, books, internet stuff, movies, etc.). I have no trouble reading ordinary stuff (news, blogs, etc.), but when I read some professional literature or some for example poetic novels I occasionally stumble upon words that I do not understand and that I have to look in the dictionary for the meaning of them (kindle helps here to not break reading flow to much).
After that introduction, my question is : is it worth and would it be functional to invest time to learn speed reading for reading stuff in English in my example, or should I first work to improve my English and vocabulary?