Learning to speak a foreign language forces one to slow down and really think about what s/he wants to say--and why one chooses to say it one way, and not another. As a writer, one with a whirlwind of words dancing around in my head at any given time, I think I took for granted the ease in which I could find just the right word. I found that, when speaking in Italian, I had to search for that word a little longer. I had to think about my use of tense. It makes me think even more about the words I use more regularly.
Learning a foreign language has also offered some fun insight on the use of coloquial language and swear words. One sees one'e coloquial language change over the years, with old words going obsolite and new words taking their place (when I was little, "totally," "rad," and "gag me" were common in coloquial speech in California, but more recently, words like "phat" and "dope" would be better received). When I think about the language cautions I learned regarding Italian swear words, I couldn't help but think about what makes a swear word; I concluded that social acceptance of a word's symbolic value is all that makes any word what it is. Strange, though, how we decide some words are dirty and others are sophisticated--and they are because we agree they are.
I wish the U.S. had more dual emersion gradeschools, as I consider how differently I would view words now, had I learned a second language back when I was a child. I find it amazing that we don't teach our young multiple languages, as great as the benefits would be.