When you are looking at an invoice, its language will be the same as the language you have set in your Settings. Similarly, it will appear to your recipient in the language they have set in their Settings.

If you have added your contact manually (because the recipient is not a Tradeshift user), you can change the language they will receive it in. Find them in the Connections page, and then click on their name or "Edit" to modify their information. There is a drop down menu titled "Language" – here you have a selection of 14 different languages to choose from. The recipient will then see the invoice in the language you selected.

If you want to print the invoice and then send it, it is possible to download the invoice as a PDF file in either the recipient's language or the sender's language – you can do that in the upper right corner of any invoice, after it has been sent.