The 11/4/09 issue of American Libraries Direct carried an item from Makeuseof.com that eventually directed me to the Transport.com website and Word of the Day in Spanish. The company offers a lot of language products for sale, but also a handful of free practical tools such as Word-of-the-Day. Spanish word-of-the-day twitter = @SpanishLanguage
School, academic, and public librarians could easily offer this educational tool as a resource for foreign or English language learners (ELL). To gradually learn or strengthen foreign language skills, it makes sense to incorporate everyday tools like Twitter, search engines, RSS feeds and such.
Footnote: Here is a NYT map of ELL titled "New to English". Visuals like this map make a lasting impression. Check it out.