No matter what reasons to take a boy off from a bar, whether sex is involved or not, you are still obligated to give him the same full tip amount that you would for taking him off for sex. Don't cheapskate him on his tip. The tip is the primary reason he agrees to go off with you. Don't forget that.
The only exception, in my opinion, would be if he knows what to expect and why you are taking him and agrees to take a lesser tip or forfeit his tip entirely. Make certain it is clear to him, fully understood, and agreed before you take him off.
Communicating with him should not be a problem these days. There are several good apps out there in which you can type in and/or speak English into the app and it will translate for him into Thai - and vice versa. He can speak into the app and what he says will translate into English. What comes out is not always perfectly accurate, but close enough.
My personal favorite translator app is Voice Tra, but again, there are plenty of others. Give them a try.