My Korean language ability is at an extremely high beginner level (venturing into intermediate?) but I will never, ever speak it in front of the class. It's often better than the English ability of many of the students that I teach. Check out A Geek In Korea's story for why speaking Korean is not such a good idea (unless you're really good). It just seems like a testing ground frought with mine-fields and potholes where the potential for me to make mistake after mistake is just too high, which makes me look ridiculous and stupid, which is something I ALWAYS try to avoid when teaching. And after all, it's not a Korean class.
However, I will use my Korean for speaking 1-1 with students who genuinely don't know English well. Like they ask me for a translation of a word, or need to talk about why they won't be in class next or something like that. Sometimes with Chinese students, it's the only way to communicate because sometimes they literally can't even read English. And, if we're learning new vocabulary that I think the students don't know already, I'll look it up on Google translate and write the Korean on the board for them. And I'll use the Korean for things like absences, attendance, future verb, etc that the students really don't know usually.