Currently I know three ways managing plugin translations, notably when their plugin:
Also the WordPress core translations have to be updated from time to time -
how to properly version them.
My current approach is to let WordPress update the languages after deploy:
wp core language update
To avoid missing language files between deploys, one could add
the languages folder to the "shared" folders that are preserved between deploys.
Subsequent language installs run very fast though thanks to composer cache.