Is it weird to contact a professor in foreign university for research internship opportunity if I am not a student?
It's not weird, but do be prepared to have your email ignored or politely declined. Professors regularly get such emails, especially if they're famous. 

In particular, what you should do is to show the professor what you can do to help them in their research. Which works of theirs are you going to focus on? What does your experience mean for the professor? 

Good luck!