In this question, we had a discussion of which languages would be allowed on Korean.SE.
The discussion mainly revolved around whether we should allow questions to be asked in Korean as well as in English. As a mod, I will let all good questions written in Korean be asked. One thing that I would ask is that we avoid asking questions in Korean just to practice our Korean. This is sort of a soft rule, but make sure that you seek to use proper grammar and spelling (Don't tell me you are a 회개사 if you actually are a 회계사. Did you eat 게고기 or 개고기? etc.).
Overall, I have the philosophy that one should use the language one is better at. For me, that is English. For others of you, that might be Korean.
However, please avoid asking, answering, or commenting in languages other than Korean or English if possible. We are sort of assuming that if you are using this site, you know one of these languages well enough to ask, answer and comment in Korean or English. Do not ask a question in German just because you can. Write in Korean or English. Is this assumption too harsh?
More However, I will myself avoid immediately deleting things written in say Chinese, Japanese, etc. I will most likely comment and ask that someone translate these comments/questions/answers into English or Korean. If no one does in a few days, I might delete the comment, question or answer. This is done to avoid unknowingly perpetuating spam questions.
There are of course exceptions. This answer is an example. Since the Japanese was relatively easy to infer from (and moreover the OP seemed to know Japanese), I will let things like this stand as is. Even I myself use hanja in my answers. (In other words, use hanja freely. But consider writing the 한글 pronunciation).
For reference, my thoughts come in part from this meta question on the French Language site (and including the links to German.SE).
Let me know of your thoughts on these ground rules.