Perhaps your customers or suppliers operate in a different language from your core staff. Set up additional templates to use for those customers or suppliers. You could create a copy of your templates as "Quote - Espanol" and "Invoice - Espanol" for example.
Much of the template can be hard-coded in their language, but the product table will need a little more configuration, making use of custom columns to define the headers appropriately.
Choose which template you want to use when you send documents by email - you'll need to do this manually, unless you have a dedicated channel for your foreign language customers, in which case you could assign the foreign templates to a channel brand for that channel.
Read about defining your own custom columns for the product table in this help center article.