What are good reasons to write my thesis in English? I'm studying in Germany. German and English are not my native tongue, but I prefer to write my thesis in English for the following reasons:


My English is better than my German (not a good reason).
My supervisor's native tongue is English (not a good reason).
I'm analyzing the socio-political situations in an Asian country. Although the official language there is not English, the bulk of the existing literature review (written by natives and non-natives) is in English. Also, English is virtually the only foreign language learnt and used over there. It's just easier to find materials in English; thus, if I write my thesis in German, it would be a laborious task to translate any cited materials. These are probably good reasons. 


Could you suggest a convincing way to word my reasons as to why I prefer to write in English? I'm filling a form of demand to write in language other than German, and they only give a small space (a line) to state my reasons. How about the following?


  The existing literature review is mainly, if not almost entirely, in English; the country's second language is also English.


Is this convincing? Thanks.
Clearly, in the time you have performing research and interacting with other people in your field, you were using at least one language, likely more than one given your research on a country that (likely) does not speak either English or German. However, your thesis has some specific audiences to address. If written in German, it certainly addresses your local university department, and the academic community in Germany. Writing it in English will dramatically broaden the potential audience, since many more people in the world can read English as compared with German. But, do those additional people count much? That is up to you to determine, and the university to agree to.

Look at your references, fellow academics you've met at conferences, and those you wish to interact with. Write in the language most likely to be accessible to them.