I taught a dog in German commands one time for the very reason that you mentioned; I didn't want just any Tom, Dick, or Harry giving him commands. Especially once I learned to have him deficate on command in the proper place!

Actually, tone of voice is important, but dogs do understand a few words when you reinforce the learning. My dog clearly knows the difference between her name and the grandchildrens' names for sure. And if I call her name, even when not speaking to her, she knows it and signals by wagging her tail.

Good luck on the training. Keep us posted.

BTW, it doesn't really matter what word you use, just be consistent. The Gaelic for sing would work as well as the word for sit. Just pick one out and be consistent. I used to use schnel when it was time for my Lab to releave himself.