That article covers how to select the language when setting up a branding theme and how to apply that branding theme to an invoice / quote.
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1. Create a Branding Theme by going to Sales > Settings > New Branding Theme.
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2. Then select the Invoices tab and select an option from the language dropdown and click Save settings.

3. When you create a new invoice, you will then have the option to select that Branding Theme. On the Edit invoice screen, select the Branding Theme you created in the previous step and click Create Invoice.
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4. Then depending on which language you selected in the Branding Theme, you will sections of the invoice translated:
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