1. Ritsu's grandmother makes a great French grandmother but she's not exactly Ritsu's grandmother any more. In Japanese- and as we see more in later books- she's a sunao uhh straightforward transparent WYSIWYG character who hasn't a clue about the odd stuff that happens all over her house. That it was she who taught Ritsu to drive is, in Japanese, a bit blinkety-blink-ohhhkayyyy moment, because ordinarily grandmothers don't drive themselves let alone teach their underage kids. One just assumes that cheerful grandmum cheerfully thinks her 13 year old grandson should learn to drive what fun for him and the underage part is just hahaha a joke on the authorities. In French it came across as sophisticated grand'mère thinks of course her adolescent grandson is old enough to drive: the next sentence- 'and my grandfather taught me about youkai from the age of three'- reads as a nonsequitur until I realized that Japanesely they both mean 'I come from a weird family.'
2. The French keeps the diminutive -chan for names, go them. Also words like kekkai and kigo, that get glossaried in the back. Go them again. OTOH Ritsu refers to the enclosed grove in the garden as 'un domain cabalistique.' The Japanese is reijou (spirit + place), which is more or less 'sacred ground'- but AFAI can see sacred because people believe it to be so rather than because someone said it was: 'an area that contains the belief and worship of people' says the J-J. I see not going with any translation that would reference Catholic notions of the holy ground, but cabalistique seems to be reaching a bit.
3. Ritsu doesn't seem quite as complexé in French as in Japanese, but in French at least there's a word for it.
ETA- and if anyone knows how to change default encoding in IE6, please tell. It's not in Internet options and it keeps defaulting to unicode. Is this because I have Japanese and Chinese enabled?