To use a lookup table in an email template, you can add the following liquid syntax to your HTML template or to an HTML element used in a drag-and-drop builder:
When used in the email template builder in an HTML block, the above syntax will render the value of the local_currency as stored under the AD object under the country item in the lookup table country-flags
You can switch to the preview section to see the output value displayed dynamically in the email template. Below, it is showing EUR as the value fetched from the look-up table.