No. Almost every MS program and course at KTH is in English, even for Swedish students. Swedish students who are doing their MS are typically in a 5 year degree program where you do your BS and MS combined. The first 3 years (BS portion) is in Swedish and the last 2 years is in English.
Excellent.
Almost every single M.sc course at KTH is in English.
Is it free for citizens to study in KTH?
yes it is (Swedish citizens)
There is no tuition fee if you are an EU/EEA/Swiss citizen.