my sister was an ex-student in ktar...
yes!! all speak mandarin!!!
even banana in ktar hv to learn mandarin if not cant communicate wit other student.. (for those reali dun understand mandarin just treat this as a learning year, at least u r good in English)
for those speak very lousy English, if u stay in ktar 2 years or 4 years.
u wont improve ur english... trust me.. at least u put effort on it..