Add a few more checks

This is a great idea.

Here are few checks that are missing
– Sanitization of data when saving to the database.
– Use nonces if not using the settings api
– Check the style.css tags
– Theme name

You might want to add a link to the localization documentation on the site.
https://make.wordpress.org/docs/theme-developer-handbook/part-two-theme-functionality/internationalization/

https://wordpress.org/plugins/theme-checklist/