Using different translation of HTML email template files

To use different translation of HTML email template files, you need to create directory for each language.

For example, when you want to translate  to Thai, you will need to create /th_TH/ in /child-theme/ultimate-member/templates/email/

and copy those English HTML email templates from /ultimate-member/templates/email/ to /child-theme/ultimate-member/templates/email/th_TH/

Now, you can manually translate the English HTML email templates to Thai.