If strings in stable are approved for at least 95% for a plugin/theme in a certain locale, the generation happens every 6 hours (00:00 UTC, 06:00 UTC, 12:00 UTC and 18:00 UTC). Then any local WordPress set to use that specific locale will download it in the next hours after the generation. Strings in readme are deployed almost immediately.
If your language translation is under 95%, you will need to manually download the strings for your language. You can export all strings but you will manually need to create a .mo file for this.
As an example, if you are wanting to get the German (DE), Deustch files for your translation, you have to actually go into the language page (ie for German):
At the bottom of that page there’s an import/export section. You can download the Portable Object Message Catalog (.po) and Machine Object Message Catalog (.mo) files by selecting those options from the drop-down and selecting ‘export’.
The files will be named incorrectly for use in your /wp-content/languages/plugins/ directory, but can be easily renamed to:
(in the style
plugin-<language code>_<language code UPPERCASE>.mo/.po and dropped in that directory and they should work automatically.