Unbabel allows you to make use of your already created templates by enabling you to quickly load them to our email composer.
Learn more about Email templates in this Salesforce KB article.
To open the template handler, find the icon at the bottom of the composer and click it. It's the same icon as the one in use by Salesforce's native feature.
After clicking, the template handler will load. You can find any Classic, Lightning or own templates, and select from specific folders. Alternatively, you can use the search field to the right to return correspondences.
Any templates matching the conditions will be listed. Clicking the template name will insert it in the email composer starting where your cursor is placed. You can freely continue to edit the message once done.