[KyleGoetz]

Nagoyankee, I've heard that using を instead tends to change the emphasis of the sentence, like maybe it emphasizes the "Japanese" (as opposed to another language). In a sense, it makes the ear jump to attention and say "wait a minute, there was supposed to be a が there!" and pay attention to the 日本語 then.

I could have been misinformed, though. It's something I think I saw on sci.lang.Japanese back in the day. I definitely always stick with が because it's safe and I don't need to worry about such subtleties too much yet.

So was I misinformed? I defer to a native speaker's experience on this one.