We can use Google Transliteration to type in Bengali on any web-site. It converts English characters to the characters used in Bengali. It offers us to type Bengali words phonetically in English script and then have them appear in Bengali. Its not translation, it does not change meaning rather it simply converts the sound of the word from English alphabet to Bengali alphabet. For example, typing "Bangladesh" transliterates into Bengali as বাংলাদেশ.
Its a small piece of code that stores on our browser(s). Visit this link to know how to enable this option to the various browsers.