At a baby shower I attended today for a Chinese coworker, I noticed the new grandmother (who was here from China temporarily) looking a little left out among all us engineers who were either talking shop or admiring the new little guy. I decided to go and talk to her, even though my Mandarin is extremely limited. After asking whether she was the maternal grandmother, how long she'd been here, and explaining that my parents were from Taiwan and I spoke Taiwanese but very poor Mandarin, I'd pretty much exhausted my conversational abilities. She said something to me which I couldn't follow; when I admitted this, apologetically, she smiled understandingly but didn't try again. I then told her I had two daughters, ages 3 and 1, although I incorrectly used nián instead of suì for "year". I couldn't understand her response to this, either, but by then my coworker had appeared to translate for me. "She wants to know if you're still breastfeeding." Well, "breastfeeding" is definitely not a word I have in my Mandarin vocabulary!
When I speak to someone who obviously has a limited command of the English language, I automatically "take it down a level"; I speak slowly, avoid long sentences or weird grammatical constructions, and use as much basic vocabulary as possible. Since this is such a natural process for me, I've always taken it for granted that people will do the same for me when I speak in one of my foreign languages. It doesn't always happen. I've finally realized that this is a habit I have because I grew up with immigrant parents and work in a industry that employs many foreigners. Native speakers of any language who communicate solely with other native speakers of that language have no reason to develop this practice. It's actually a skill, being able to make oneself understood using only "basic tools".
I had a boyfriend in high school who, upon meeting my mother for the first time, decided that the way to impress her would be to show off his intelligence by using lots of big words. Although his intentions were noble, he ended up making her extremely uncomfortable because she could hardly understand what he was saying when he used words like "teetotaler." He'd meant well, but I didn't appreciate it at the time; I was just furious with him for not doing what I thought was obviously the considerate thing, i.e. accommodating my mother's limited English abilities.
Some might say that this practice is a bad one, that it's condescending, or that speaking above a person's level only serves to teach them. But I believe that the primary purpose of using a language is communication, not instruction or avoidance of offense. A person who is learning a new language is much more likely to feel happy about it if he discovers that it can actually be useful in the real world, rather than if he thinks he's doing well but can't seem to carry on an actual conversation with anyone. So I'll continue to take it down a level when I speak with foreigners in English; I'll appreciate it if they do the same for me in their native languages, but I'll understand if they don't.