By attributing certain clients to a department you can personalise specific e-mails in specific languages.
Add a new department and configure the default invoice language and e-mail template by going to Settings > Company / Department > Separate Configuration for Documents Via E-Mail Auto Payments should be enabled, if not please enable now (Settings > Account Settings > Auto Payments) then attribute the products sold and to be sold to that department by going to Warehouse > Products > Select Product > Edit > Auto Payments > Check Online Sales > Department Issuing the Invoice
In order for your clients to receive an invoice after their payment has been made you enable the feature in Settings > Online Payments > Automatic E-Mails > Send E-mail
After Payment is Made to in Accordance with Invoice Sending Template