earning to speak Thai reasonably well is the only way to interact with the Thai people and actually get to know and understand the culture - because most Thai themselves only have superficial English language abilities at best (with a few gifted exceptions, of course). It's the only way to properly bridge the gulf between two very different worlds and lifestyles. Personally I find a lack of decent command of the relevant language makes a stay in the country somehow incomplete. Something important is missing.
Plus, of course, I think the effort to learn the language indicates respect for the country and people concerned.