That is normally a job that is undertaken by translation agencies that specialise in working with RoboHelp, they have special tools for the purpose.
Beyond that tools such as Beyond Compare would tell you the files that have differences but here again you hit a problem. You are working with different versions of RoboHelp so the code will likely be different even where the content has not changed.
Maybe someone with more translation experience can suggest something but it maybe you have painted yourself into a corner.
Also take a look at Ben Minson's article. http://www.adobe.com/devnet-archive/robohelp/articles/localized_projects.html
See www.grainge.org for RoboHelp and Authoring tips