Dear Katarzyna,
the best address to contact is the International office. They can tell what the formal requierement are. Here is their webpage, where you can find information and email addresses: http://www.rwth-aachen.de/zentral/dez2_english_leitseite.htm
Generally speaking (but please confirm this with the International Office, I'm only a student myself!), there are no tuition fees, exept a fee of about 120 € (this includes a bus ticket) for each semester. I don't know whether there is any chance to get a scholarship, exept an ERASMUS scholarship which would be granted from your home university. I think, it should be possible to come a as a "free-mover" (without being sent officially by your home university), but again, the International Office will know more about this.
For the English Department, nearly all courses are in English, there are only few exceptions. Unfortunately, I don't know whether you need a certificate about your German or English.
The International Office will also be able to give you more information on how to apply for a place in a student house, when the deadline is and all other official stuff.
The curriculum for English linguistics you'll find under: http://www.rwth-aachen.de/anglistik/en/index.html (click on studies). The German university system does not distinguish between years. Here, you have to do "basic studies" (Grundstudium) (usually four to five semesters) and then "advanced studies" (Hauptstudium). To be able to enter into advanced courses you have to pass the "intermediate exam", but most exchange students mix courses from both basic and advanced studies or stick to basic courses only. But you can discuss this with the tutors personally upon arrival. There is no fix timetable, you can choose what to do.
There is also the study advisor for English studies, she can give you exact information on what requirements you'll have to fullfill to be able to enter advanced courses. Here is her email address: mirbach@anglistik3.rwth-aachen.de
I hope that this helps a bit.
If we can be of further help, just mail again.
Kind regards, Britta Weber (student representative, Department of English, Aachen University of Technology)