Feat: Improve check translations script with Coverage and Completion metrics

[choo121600]

I think previous i18n check script's output confusing. When I saw the "All translations are complete and consistent!" message along with a 100% progress rate, even with many TODOs remaining, I mistakenly assumed that the translation was fully complete.

This PR enhances the script to provide a more accurate and nuanced status by introducing two distinct metrics:

• Coverage: This would confirm that the key is synchronized between the en and the target language.
• Completion: This would measure the actual translation progress by checking for keys that are no longer marked as TODO.

closes: #53324

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[potiuk]

Cool. Tested it and works great :)

[github-actions]

Backport failed to create: v3-0-test. View the failure log Run details

Status	Branch	Result
❌	v3-0-test

You can attempt to backport this manually by running:

cherry_picker fa60229 v3-0-test

This should apply the commit to the v3-0-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue