en-US at the beginning of a Yaml file doesn't get changed to fr-FR. I've got this Yaml file:
en-US:
account.accountdetails.title: Account Details
account.accountuserlist.title: Account User List
account.activitytypes.title: Activity Types
account.exportusagereports.title: Export Usage Reports
account.advancedsecurity.title: Advanced Security
....
Development needs the en-US changed to fr-FR. Passolo doesn't do that.