Ah? In that case, the same applies, with a reservation. It's better to use English with special characters to denote the use of foreign language, and show in the story that it's incomprehensible to the other characters, unless you want to have an effect of keeping the readers in the dark too.
Oh, I definately agree with what lwf58 says here. But I've seen this way overdone as well, in where an authour will use a differant type of quote system for thoughts, sounds, chinese, french etc etc etc. All of that stuff just clutters the text, and makes it hard to read.
If you want to use translated foreign languages, use <these types of quotes> for ALL of the languages other then the main. Use the reactons of others or add it into the description as to what language it is, similar to lwf58's example.
Sound effects HAVE NO SPECIFIC QUOTE SYSTEM in normal prose. Don't create one either....
Thoughts, on the other hand, DO have a system. Generally
thoughts of characters in prose are in italics, like this. Again, don't fix what ain't broke.
But, to get back on the main topic, I see nothing wrong with a character speaking in their native tounge in a story, since that's what happens in real life. Just take care in HOW you portray that use of language... that's what I have an issue with.
Oh, and exact literal translations (the Kasumi-oneesama example) are just plain akward most of the time. Prose needs to flow, and literal translations usually just don't work, nor do they convey the proper connotations of the word or phrase. Nothing wrong with using the proper names or honorifics, so long as the meaning and connotations behind it are made known somewhere else in the text. With reluctance, you can do this with a footnote / glosssary, but it is much smoother and better to find a way to put it in the main body of the story somewhere.