Translations using XLIFF

My client has advised that they want to manage translations in the same way that a translation agency would.  I am trying to accumulate information on how this can be done to help make the transition easier.

Apart from exporting the translation file from Storyline as .xliff, I have no idea what to do next and what software would be needed.  I found an article online regarding Rainbow/Okapi and am wondering if this is the required software.

This is a long shot, but I'm reaching out to see if anyone knows the process from beginning to end.  My client is of the opinion that this will save pennies and valuable time if they can do this themselves.  I am skeptical, so really need to know the ins and outs before a decision can be made.  

Unfortunately this has come about due to the extortionate rising costs of translating material through established agencies.

Thank you all in advance.