Some schools for certain languages run special Christmas holiday courses, so it's not completely out of the question that you'll find a course. (I'm more familiar with Christmas courses in Spanish, though.)

I've taken a lot of language holidays (in fact, I just got back from a week in Barcelona) and I think they're a great way to brush up your skills and enjoy a solo holiday.

If you have studied German before and want to refresh your skills and advance a little, I would recommend either that you study a little before you get there or that you take private lessons. Otherwise, you're likely to get dumped into a beginner or near beginner course with a group of students who likely will be progressing fairly slowly because they're learning for the first time something you learned once before. That's the reason I took (relatively expensive) private lessons during my last learning holiday in Barcelona. I didn't have time before I left to study much, although I did re-read about half of my "Teach Yourself Spanish" book. My teacher at the Don Quijote school told me that, on arrival, I tested at about the low "A2" level (with A1 being the lowest and A2 being the highest, and A2 normally taking about 75 hours to complete). She said that the end of the week (20 hours of private lessons), I tested at the mid-B2 level (i.e. completed A2, then B1 and started on B2). Money well spent, I thought, for an efficient learning experience.

So, to get the most out of your two week course, try to find the time to review the basics before you get there. I found that the "Teach Yourself" series is a rather painless way to refresh your knowledge - and it's an easy book to read e.g. on the commute to and from work. Other options are exercise books designed to provide a review of high school or college level German (e.g. Schaum's Outlines) or verb review books (your knowledge of verb tenses is typically one of the most important elements they test when you arrive for a course).

I know that in France, there is a "quality association" of French language schools where the schools subscribe to a charter regarding teaching standards, transparency with respect to the program costs and components, etc. I'm sure something similar exists in German. Such an association also likely has a website that lists the schools, and that can help you find the right school with the right schedule for you.