t3h = the
It would have been rude for Masamichi to ivite them both to dinner in japanese, since largo doesn't understand japanese - he switched to english once he got the impression that it was true that largo and erika were dating. For largo, he went from understanding nothing of the conversation (after what piro translated for him) to being invited to dinner with erika. I think its reasonable to assume that he'd be confused by all of this.
(btw, this really is the problem with not showing every minute and every reaction of everything that happens - i try to montage a little bit to keep things going and people get mad at me for the gaps :P Ah, the balancing act of keeping things going...)