FAs are not rude/impolite, they have just have limited English skills and you get the feeling that they don't understand you or do not know how to respond. Most of them seem to be unaware of the service concept (how to serve a passenger with a smile and a friendly chat etc) but that is most likely due to inexperience and inadequate training by TK.
Do keep in mind that TK has been expanding a lot and hired many new FA, so most of them are inexperienced and not yet gained the confidence and knowledge required to serve pax in a professional manner.
Except for the crew everything else on TK is perfect. Great food, nice seats in C and CC, great IFE, the best lounge in the world at IST etc. I would not hesitate to book TK again.