Translation string "GRAV.YES" for Checkbox in `forms/data.html.twig` not working

I am using the `forms/data.html.twig` to render form content inside a confirmation email.
When there is a checkbox, the value (so either `GRAV.YES` or `GRAV.NO`) is not translated. Do you have any idea what the reason could be?

Start with forms/data.html.twig and reproduce a checkbox value in a confirmation email using the reported form setup. Trace how the GRAV.YES or GRAV.NO value is rendered and translated; done means the checkbox value is translated correctly in the email.

Written by the indexing model from the issue text.