Google Transliteration IME

How does an IME work in general ? Google Transliteration IME have many local languages. We type in using roman keyboard the sentences in one of those languages and the script changes to that language. What is the principle behind it. Is it like having a massive dictionary of words? What is your idea regarding such method?

[edit]
I have problem with posting this question. At first I gave the title as “How does Google Transliteration IME work?” It simply shows a blank page like the one that IqAndreas was talking earlier. Later changing to the above title worked Spam control? But not very efficient anyway.