So, you find yourself in Equestria and the ponies do neighs and other pony noises, completely incomprehensible to you, but are otherwise friendly.
At night you are visited by Luna in your dreams and she gives you a choice:
1) She can cast a spell on you that would assign the various words etc from your native tongue to their native tongue. This would make it far easier for you during your stay, but you would lose the ability to speak your native tongue pretty much permanently (you would have to relearn it if ever a way was found to send you back). Because of how it worked, it wouldn't be a good idea to try it a second time.
2) You could stay in Equestria while they worked on a way to get you back, but you would have to learn their language from scratch and it would not be the least bit easy, the languages being so very different from each other, and you would be stuck not being able to communicate at all to begin with and managing only the basics for a very long time. Even then it would at best be a difficult/alien second language to you as opposed to being a native language like you would have in 1.