I might understand French moderately well, but I would hesitate to claim knowledge of French

I understand what you're getting at, mav...

But I don't think you'd claim "knowledge" of French. You may claim knowledge of the French language, but even then, that wouldn't necessarily mean you understood French - it may just mean you've read lots of books on French grammar.

It seems to me there's something more dry about knowledge when set next to understanding. And language is more of an ocean than a desert, as I'm sure you'd agree.

However, I agree with you on the debasement of the word 'understand'. Not that that's the only word to have been thoroughly debased in the wonderful world of business!