I was doing my visiting teaching this month and the lesson's focus was on eternal families. The entire family had gathered to hear the lesson and my companion hadn't showed up yet. So, as I began teaching the lesson I was attempting to make the comment that joy comes from our families and that Satan is miserable partially due to the fact that he cannot partake in the joy of family. That is what I MEANT to say... this is what I said, "Satanas tiene mucho misercordia porque el no tiene una familia." - at this point the family started looking at me strangely and because I am learning this language and I am a foreigner here I could read that expression in a minute! I knew I had said something incorrect. But, I had NO idea what. Then, the sweet sister asked in halting English if I meant "miserables" (misery) and I realized what I had done; "misercordia" is mercy and "miserable" is misery.
So, the tip of the day is when teaching a religious lesson in another language it is always wise to make sure you have your adjectives correct and don't speak a word until your companion is there to correct major errors regarding gospel principles!