Just to clarify on the whole "zilla/zirra" thing:
The reason it's like that is because in Japanese (and possibly some other Asian languages; I don't know), the "r" sound isn't like an English "r," but is a blend of the English "r" and "l" sounds. There is no "l" sound in Japanese, which is why some native Japanese speakers misprounouce (to our ears) words with "l."
</language nerdiness>