Yes, you can translate your documents in any language you want.
For that, you have to go in Settings > Document and email configuration. You create a new configuration, you give it the name of your choice and you provide the translations of the fields appearing in the documents (in the Translations tab). You can also define the localization settings for this configuration, the terms and footer you would like to add, etc. (see the other tabs).
You can create as many new configurations as you like. To define a configuration as the default configuration (which will be used when you create new clients), click on the yellow star.
Once you’re finished, don’t forget to go in the Clients tab and to select the right document configuration for the clients concerned.