Translation is done via the Transifex service:
Log in to: https://www.transifex.com/openmrs/
From the Home page, select one of the ESM projects (likely one that you’re distro is using):
Eg: openmrs-esm-patient-management

Click on Translate:

Search and select your target locale and then the resource you want to translate:
Eg: French (fr)

Select a row on the left panel and provide the translation on the text box next to it, then Save Translation:
Eg: Add Relationship

Once all strings are translated, they must be reviewed.
This can be done either one-by-one or in bulk.
One-by-one: