Based on what I can tell, non-Latin characters will display fine if the page (or server) declares the correct character encoding (and UTF-8 seems to always work well), but when no character encoding is declared, then it is necessary to manually specify an encoding using the browser. So yes, this is definitely a needed feature if good internationalization support is desired (and it should be).
A rather minor issue that I've noticed is that, even when the page itself displays non-Latin characters correctly, the tooltips used for ALT text may not. This is also true of the title bar and the layer label. A good example is here:
https://es.3ds.verifiedbyvisa.com/enrollment/enrollCardholderPan.jsp?preferred_language=ja_JP
(This page should use UTF-8)