Translation files can be reloaded without upgrading the add-on modules by repeating the Load a Translation action. This can be used if you have updated translation files and don't want to go through the trouble of upgrading the modules (and all their dependencies).

If the Overwrite Existing Terms checkbox is left empty, only the newly translated strings are loaded. Thus, the changed translated strings won't be loaded. Check the box if you want the already existing translations to also be loaded and overwrite the currently loaded translations. Note that this can potentially be problematic if someone changes the translations manually through the interface.

The previous checkbox exists because we can edit specific translations by going to the Settings|Translations|Application Terms|Translated Terms menu item, or by using the Technical Translation shortcut option in the Debug menu. Translations that are added or modified in this way won't be overwritten unless the language is reloaded with the Overwrite Existing Terms checkbox enabled.

It can be useful to know that add-on modules can also have an i18n_extra subdirectory with extra translations. First, the .po files in the i18n subdirectory are downloaded. Then, Odoo ORM downloads files for the base language and, after that, for the language variant. Following this, the .po files in the i18n_extra subdirectory are downloaded, first for the base language and then for the language variant. The last string translation that's loaded is the one that prevails.