Translations are managed under 'company data'. For translations to work, a spreadsheet with a list of translations, plus a sheet with a list of languages needs to exist.
Translations data source:
Term: Reference to the placeholder in the template that needs to be translated.
IANA: en-GB, de-DE, etc. refer to the language choices made in a User Profile.
Language: List of languages that the User can choose from.
IANA: en-GB, de-DE, etc. refer to the column in the translations data source.