You can change the invoice and proposal fields to say whatever you'd like, in whatever language you'd like! Just go to Settings > Label Translation and change the text for the fields you'd like to customize.
For example: - Change "Unit Price" and "Quantity" to "Hourly Rate" and "Hours" if you charge based on an hourly rate. - Change "Reference Number" to "Order Number" if that's how you track invoices. - Change "Proposal" to "Purchase Order" if you want to use our Proposals as POs. (More info here.)