But by langcodes, when i type "How are you", the code is passed to the user and he sees it as "AAp kaise hain" in devanagari script.
That will involve tranlation and translation is pretty tough, not to say tough to achieve under real time.
Also say ur browser supports 5 languages, then u gotta have 20 (5 x 4)translation engines. one way to get around this complexity will be to convert the input language to a language independent intermediate format and then from this intermediate format to the final language. in this case you just gotta have 10 translation engines, and the savings get greater as you start supporting more languages.
There is work being done for developing an intermediate languae (UNL, Unified Natural Language). But this brings along problems of its own. In India IITB is involved in developing engines for Hindi to UNL and viceversa.
regards, Martin.