Update i18n freeze instructions

[shahar1]

Copilot Summary

This pull request updates the i18n (internationalization) release workflow and documentation to clarify the process for translation completeness checks and translation freeze periods. It also improves the CLI output for translation coverage. The changes aim to make the release process clearer for both major/minor and patch releases, provide more actionable guidance for contributors and translators, and enhance communication around translation status.

Documentation and Policy Updates:

• The i18n workflow in dev/README_RELEASE_AIRFLOW.md is rewritten for clarity, distinguishing between patch and major/minor releases, and providing detailed instructions and communication templates for each. The process for announcing and managing translation freezes is clarified, including when freezes are required and how to lift them. [1] [2] [3] [4]
• The definition of an "inactive owner" in airflow-core/src/airflow/ui/public/i18n/README.md is updated to refer to two consecutive major/minor releases instead of just "releases".
• The section on translation freeze in airflow-core/src/airflow/ui/public/i18n/README.md is revised to clarify when and how freezes are announced and enforced, and to specify that freezes apply to the default (English) locale files.

CLI Output Improvements:

• The check_translation_completeness command now displays the median translation coverage across all languages in the summary table, and uses improved color coding (green for ≥95%, yellow for >90%, red otherwise) for easier visual assessment.

These updates together make the i18n process more transparent, actionable, and user-friendly for both release managers and translation contributors.

---

^ Add meaningful description above Read the Pull Request Guidelines for more information. In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed. In case of a new dependency, check compliance with the ASF 3rd Party License Policy. In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[choo121600]

Aside from one question I have, everything looks good to me :)

[github-actions[bot]]

Backport failed to create: v3-1-test. View the failure log Run details

Status	Branch	Result
❌	v3-1-test

You can attempt to backport this manually by running:

cherry_picker d8604c4 v3-1-test

This should apply the commit to the v3-1-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