Create language overrides for the message in any language you want them translated in. See the below on how to use language overrides.
www.joomlapolis.com/blog/kyle/18701-language-overrides-have-arrived
Some language plugins may already have translated that string as well so be sure to install whatever language plugins you need.
That's the CB Invites email message body though and that's a parameter so if you changed it from its default it won't be translated by language plugins and you'll need to be sure to supply language overrides for your custom string. Emails should send in the language of the recipient user, if there is one, otherwise will be in the language of the sender.