hey, back to the original question of this post.
Sometimes I'll remember conversations I've had, and even remember most everything we discussed, yet I won't remember what language we discussed it in. Sometimes I can figure it out through deductive reasoning (i.e., we only have one language in common). But other times, if we have more than one language in common, and are known to switch quite freely, or if I didn't know the person that well and so can't remember what langauge they spoke, then even though I remember everything about the conversation, I don't know what language we were discussing it in.