You're pretty much dependent on whether the user's particular browser wants to support that feature, although there's a server-side element as well, in that the browser and server can negotiate NLS support. Apache has pretty good docs on how this can be configured - I haven't studied what might be in any
J2EE servers, but I did notice that there's a setLocale() method for serlvet responses to allow for proper formatting of dates, currency, large numbers, etc. (this also sets the charset in the content-type header).
You'll probably also want to pay attention to the language-code and charset options of the FORM tag - this is where you'd have to let the browser know what to do with the input tags as far as selecting character sets and directionality (if the browser supports them).
You might also want to snoop the html generated by Arabic websites to see what they're using.
Finally, don't forget that if you are persisting the data, make sure your DBMS supports NLS and is set up to do so!
Good Luck (or maybe "hattan sa3id"!)