Someone brought up Claudia and Janine potentially learning some Japanese from Mimi in
a thread the other day. I've found an answer! Normally, I'd keep a comment to the entry, but a lot of people seemed interested in the topic. The post is a little ways down the front page, and I figured it'd get lost.
I was reading Shannon's Story just today, and I came across the following passage, coincidentally:Claudia rolled her eyes and grinned. "I can understand some Japanese because my grandmother Mimi often spoke it. But I can't really speak it. When it comes to Spanish and French, si and oui about does it."
Earlier in the book, Janine also responds in French to Shannon "without missing a beat," so she's apparently good with languages in addition to being a math/science/computer genius. I can definitely see her knowing Japanese, but we don't really get enough of Janine in the series to see that.