Change vendor default settings
Go to the vendor profile you need, scroll down to the Default settings section, and press "Change default settings":
It will display the Change default settings page where you can set your vendor's default currency, payment conditions, and the PDF locale of invoices:
Note: Payment methods can be created in the Payment methods settings.
PDF locale of vendor invoices
By default, the system uses the locale (language, date and time) of invoices specified in the "Default settings of your account whenever vendor invoices are generated.
But here you may define the different one only for this particular vendor.
Note: The PDF locale setting defined in a specific vendor's profile overrides the default one specified in the account default settings.