You can change system email templates (of messages that will be sent on your behalf by CoachAccountable) so clients will read your messages in whichever language you write them in. Likewise, all of your written content and communications with your clients, such as Whiteboards, Messages, Worksheets and Session Notes can  be written in your language of choice.

With the bulk of your client-facing content that is specifically to do with your clients working with you in your language of choice, the only thing that remains are the actual UI bits of CoachAccountable, menu items being the most significant.  If you can explain and translate those to your clients, in particular the key participatory bits like Stream, Actions, and Metrics, they might be very much able to use the UI as is.

Creating and sharing with your clients a Whiteboard containing translations of key items can go a long way.  You can make this as a template in your own coach dashboard and then readily clone it to your non-English speaking clients.

As mentioned above, your templates for outgoing system emails can be customized fully and thus written in whatever language of choice.  If you have a multitude of client languages to support, Team Edition provides a nice way to segment those templates along those language lines.  The key is that every coach is allowed to customize their set of system email templates.  The templates that a given client will see are generally that of whomever is that client's primary coach.  Therefore by pairing clients with the right coach, they can get system messages that are in the desired language.