Question PM and 2 Languages

Is there any PM feature that I can use?
Do I need to install additional component?
Appreciate if someone can show me how to add this into my forum

Another question, I'd like to make my forum have multi-language
function. That means when users choose the language - the system
message and menu will appear accordingly. Is there any way
I can do so?

You can use uddeIM, jomsocial or even try with clexus for your PMs, these are all 3rd party extensions

For language, yes, kunan picks tghe language your user has selected for joomla, and applies it also to kunena, if you have it also, and shares name (eg: joomla lang name is german, kunean must have a kunena.german.php file

Thanks for the prompt reply.
May I ask which of the PM extension is better? I need a stable 1 with normal feature will do.

Not quite understand the language thing you mentioned above. Does it mean I have to download a language file and install to my joomla? If it's the case, how to do so?

Thanks!!

if you just want PMs go for uddeIM, clexus has been discontinued, and jomsocial is a paid complete commjunity system. If you plan to use CB, or just want PMs, uddeIm is for you

joomla has languages as well, so, yes, you need to have joomla language files, and kunena language files

your users can select wich language to use in your site, from the ones you have installed, from a dropdown box in their joomla profile

Thanks. How about to let users chooose at the main page instead of
going to the user profile?

Sorry for asking too many questions