^ Tread carefully (pun intended).
I'm a 45 in MMM and everything else, I had a pair of 10UK Lanvin sneakers (velcro strap circa fw09) that were too small, they were really uncomfortable after the first 5 minutes worn (which I didn't realize when I bought them on sale) so I sold them, but I also have a pair of 10UK Lanvin boots that fit great, really comfortable just on the snug side.
Size-11 Lanvins I've tried on (which should be my equivalent size) have ranged from perfect fit to "a bit too roomy."
TLDR = a Lanvin 10 may or may not work out for a 12US, but I wouldn't gamble much money on it.