Put the language MO files inside this repository (?)

[jnm]

Django itself stores .mo files in git. We could do that too and get rid of compilemessages as a build step.

Originally posted by @jnm in #3820 (comment)

Further thought 1) compilemessages has lead to some "why does my build not work today" issues seen on internal chat when something is wrong with translations. I'd rather see this done in a CI bot or manually on some schedule. Storing the mo file in git is fine. It's storing a snapshot of the translations at a point in time. Maybe it's not perfectly normalized as it's really a computed value, but it's good enough and the mo files do have unique meaning in that they are known to be working translations.

Originally posted by @bufke in #3820 (comment)