Language in martial arts gyms is a funny thing. For us, we speak English, and we train in English, and there is a reason.
Over the years I've seen and been guilty of some terrible misuses of language during my training. Coming originally from a Karate background my decision to teach in English came, oddly enough, after taking a Japanese language course.
So let's start with some examples:
First, a obvious one, and one that I mentioned in a previous post on titles. "Sensei", in western schools this is treated as a title meaning martial arts instructor. But it's not a title, it's a honorific term. It is used to refer to teachers, as well as anyone in a position of authority. So if you're talking to your lawyer, it would be appropriate. If you are a 20 year old karate instructor teaching a lawyer, you'd probably be using it towards them, not the other way around. A person would also never introduce themselves as "Sensei Andrew", or put it on a business card (which gets done over here all the time), it's something others use towards you. There are teaching titles in Japan... "Sensei" is not one of them.
And now a funny one: In Japanese "Mae Geri" roughly means front kick, "Yoko Geri" side kick, "Mawashi geri" is a young kick and so on. So "Geri" means kick, pretty obvious. Except it's not. "Geri" means diarrhea. "Keri" means kick, unless it comes after another word, then it becomes "geri".
I'm not sure why in the west we like to try and use... and end up misusing foreign language as a part of training. I imagine some feel it gives their training some sense of authenticity. But without context it is so incredibly easy to misuse language in a way which I think is disrespectful to native speakers, especially when we teach it as part of classes.
The other thing to keep in mind is this didn't really happen with the countries of origin for those systems. Karate used Japanese, not Chinese when the Okinawans imported things. When Koreans learnt karate during the occupation they went back to Korea and taught using Korean and renamed everything. (Granted Korea was pretty anti-Japanese in general at that time.)
Some things have names in a language that don't really have a direct translation or a name in English. In those cases it makes sense to import the word, and thats what is generally done outside of martial arts. "Sushi" is still "Sushi", we don't really have a English word for it. It makes sense to use "Sushi" instead of inventing a new one. But even when we go to a Japanese restaurant most of us still call "rice", "rice" because we do.
Anyways, one more, "Osu" and I'll leave this one to a link: http://www.karatebyjesse.com/meaning-oss-osu-japanese/ the amount of "Osu-ing" that goes on in some places is almost silly, using it as a general word for everything possible and thinking it is respectful. It's a "low class" word, and IMO has little place in a educational environment.
Anyways, we speak English. Hopefully we are able to get that language right. :)