First of all there is no way to localize a RoboHelp project. Even if there was I wouldn't allow anyone to use it The subtlety of grammatical rules and meaning is very easily lost when attempting to automate translation. You should start checking out this link on the RoboHelp Developers Network which deals with the topic.
I should add that whilst the article is old, a lot of the advice still applies. The functionality in RoboHelp has also advanced over the years to handle diffferent languages in your project. There are a number of resources around that touch on this including my own blog.