Import your own interface translations automatically during profile or module installation
To import your own translations you should use the interface translation properties on your module.

I'm using a folder translations in my modules where my language files like de.po or fr.po can be found. To load the translations you have to insert the following lines into your example_module.info.yml:

'interface translation project': example_module
'interface translation server pattern': modules/custom/example_module/translations/%language.po


And to update your translations use this:

drush locale-check &amp;&amp; drush locale-update &amp;&amp; drush cr


EDIT:
To update existent translations you should take a look at the settings page (/admin/config/regional/translate/settings):



You can try to use local translation files only or to overwrite any existing translation.