To create and customize templates for order confirmations, order comments, and additional print templates, you can navigate to Configuration -> Settings -> Advanced-> Notifications.
Framework templates and additional templates
We categorize them into framework templates, which are used for order confirmations and order comments, and additional templates, which are used for prints.
Defined for each market
The templates will only apply to the specified markets. To use the same template for all markets add the same template for each market in the market tab.
Further Reading: Template creation guide