Send introductory email to foreign university professor ahead of classes
My advice is: Do not do this if you just want to introduce yourself or establish a line of communication. For those purposes, just talk to the professor in or after class or leave it all together -- just like the professor wants.

If you have more practical reasons (like if you need to review someth.), do this before and per email. (I'm assuming here that you read all inform. about the courses and do not ask about information posted e.g online.)

If you think there is a chance the courses could not be in English, I would also advice you to ask beforehand. (If the program is advertisted as being in English, I think you should not ask.)

If you send something, I would advice to speak with your classmates and send it together with them (in all their names, after they agree). This advoids you to be seen as a social weirdo who secretly wants to get advantages - after all, the information is important for everyone and you want everyone to have a great experience.