Hi. I am programmer in Japanese.

I think that I also want to contribute to a great product called Mattermost, I am writing this in poor English. please forgive me.

My suggestion is "Mattermost/doc i18n support". Mattermost/doc using sphinx, because I thought that can be easily implements with "sphinx-intl".
ref: http://www.sphinx-doc.org/en/stable/intl.html

I made PR (protorype), I hope you will discuss it.
https://github.com/mattermost/docs/pull/80

sincerely.

p.s.

This is my first contribute working, and my English is so poor, please forgive me if I say something rude.