Number of 4-letter words, including repeated letters, using a 26-letter alphabet=264=456976.
If no repeated letters: 26×25×24×23=35800.
Not all the world uses alphabets (like Japanese, Chinese, etc.) and alphabets can't be mixed (Latin, Cyrillic, Hebrew and Greek for example share some symbols but others are unique to the language). So I've just used the standard English alphabet.