Many people think it is pretentious to use Japanese terminology when there's a perfectly good English expression for it. However, if you were to go to train in Russia, or Holland, or Brazil, or Japan, or any other country where English is NOT the primary language, your anglophilic arrogance would be taken down a couple of notches, because you wouldn't understand a word of what they're saying. Of course, Japanese spoken badly with say, a Russian accent is probably hard to understand when you're used to Japaneese spoken badly with an English-based accent, but it's still a lot easier to get used to than having to learn all the terminology in Russian. And then next year on your next holidays, you might have to do the same thing in Dutch when you visit Holland. Dutch-accented Japanese would be far easier to learn. You may still not be able order food, discuss the weather, or have heated philosophical debates, but you will be able to train. After all, isn't that what's most important?
This is probably also a good reason to try to learn how to say the words correctly, and not mispronounce the words that your instructor is teaching you, which he is probably already mispronouncing. A good example of this comes from personal experience, and the discussion boards on this site managed to unravel it for me. My instructor says something that sounds like "sonesteh" when it is time to tidy up our dogi, and this was duly noted with the spelling "soneste" in our vocabulary handouts. I asked around on my discussion boards to find out if that was correct. NO ONE knew what it meant. People offered me dogi na(o)shite, or fukuso na(o)shite as options, meaning tidy up your dogi and tidy up your clothes respectively.
As it turned out, it must have been derived from the latter expression combined with and a severe case of chinese whispers. In Japanese both "u"s in fukuso are barely pronounced, resulting in a word more like fkso. Also, the i in naoshite is not normally pronounced, and the o is also glossed over. The e on the end is pronounced as in eh. So in Japanese it sounds more like nashteh. Add them together to get fkso nashteh. However, since most English speakers have problems pronouncing words that begin with consonant combinations like fks, the first two get dropped and there remains so nashteh. Join them together, and add in a bit more chinese whispers, and voilà, you have sonesteh!
A globally common set of terminology, if used correctly, is
a very useful and necessary thing. In ballet and fencing, it's French,
in computers, it's English, in music, it's Italian, in Capoeira, it's
Portuguese, and in biology, it's Latin. These are all largely based on
the language in which the particular discipline was founded. In karate
therefore, it's Japanese.