1. The most obvious disadvantage of a student exchange program is the cultural shock that any student has to go through. For instance if a student from Germany has to shift for an exchange to China and the vice-versa, it is going to be a big challenge initially. You need to be acquainted with at least one of the official languages of the host country otherwise it would be difficult to stay there.
2. Next fact that you will discover is that the family that your going to live with is firstly not yours and has a very different routine unlike yours. So, you will have to adjust or compromise with their habits. Though it is not that dreadful, as even the host families understand that the person who has come from a different place must have a different lifestyle. So, probably you need to find a midway that works for both of you.
3. Time zone difference : Though it is not that big issue but it is definitely is a big problem during your initial days in your guest country. So, try to get accustomed to the local food and the timings so that you adjust with the standard time and routine