For the item: Ring of Sustenance. I won't have to spend money on food ever again, and I'll only need 2 hours of sleep per day. This is a must for a teacher.
For the ability: Polyglot. I'd be able to speak, read, and write all languages (not including magical script). So, I guess that means I won't be able to read the Bible, or the Koran, or the Torah, or Harry Potter books.