Invoices must have correct attributes attributes like Firm name, Firm address and VAT number. Currently no one European goverment Tax/revenue department will accept invoices without these attributes.
Dates also can be set to be displayed in EU format DD/MM/YYYY
You can specify account name under 'Profile->Edit Profile' and that name gets printed on the invoice. Additionally users can also under 'Billing->Billing-Settings' specify the address and VAT number. This information is also automatically printed on the invoices.