I think the Cyrillic alphabet has enough overlapping letters with the Latin alphabet, that it's relatively easy to learn the other. Possibly the Greek alphabet even overlaps better with Cyrillic than Latin?

Try Arabic, though. I took a relatively intensive four-week Arabic class one summer, and we spent the first week or two on the alphabet.

Anecdote: when I was little (in the USA), our family had a big dictionary, and in the back was, among others, the Cyrillic alphabet along with how to pronounce the letters. I would write out English words in Cyrillic letters, thinking that I was writing Russian words. :)