The CoachAccountable UI is only available in English. However, English speaking coaches have had success making CA work for their non-English speaking clients, because so much of the content that a client sees is whatever content the coach set up for them.
Making CA Work for Non-English Speaking Clients
You can change email templates of 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.
You'll find a more detailed guide into this approach of using CA with non-English speaking clients here.
Browser Based Translation
It turns out browser-based translation is getting quite good and reliable. Therefore for a complete translation of the CA UI, you and your clients can translate the entire site using Google Chrome. Here's a step-by-step on how to set that up.