Neat idea. It may also be interesting to see whether existing open source tooling could be used or combined with Rocket.Chat. The latter obviously requires more effort.
I haven’t had a deeper look into the world of community-sourced FOS web-based translation software but I think it might be worth to look around. From a quick search only I came across this:
http://pootle.translatehouse.org/index.html
But I think there are at least two others worth looking at 
Cheers
Thomas