Upgrade/Install: List available translation updates on the Updates screen

[s-a-s-k-i-a]

Trac ticket: https://core.trac.wordpress.org/ticket/42281

Summary

list_translation_updates() currently renders only a generic "New translations are available." message and the Update Translations button. Unlike the WordPress core, plugin, and theme update sections, it does not resolve or display the specific translation updates that are pending, so there is no pre-upgrade visibility into which component/language/version combinations will be updated.

This PR adds display helpers for translation updates and uses them on update-core.php to list the pending translation updates before the upgrade runs.

Changes

• add translation update display helpers in wp-admin/includes/update.php
• resolve translation update names for core, themes, and plugins
• map plugin translation slugs back to installed plugin files so WordPress.org-style slugs still display the correct plugin name
• display a translations count and a per-update list on wp-admin/update-core.php
• add PHPUnit coverage for translation update display data, including plugin slug fallback behavior

Test plan

• php -l src/wp-admin/includes/update.php
• php -l src/wp-admin/update-core.php
• php -l tests/phpunit/tests/admin/includesUpdate.php
• vendor/bin/phpcs --standard=phpcs.xml.dist src/wp-admin/includes/update.php src/wp-admin/update-core.php tests/phpunit/tests/admin/includesUpdate.php
• Authenticated HTTP smoke test against https://wpcore.wp-studio.dev/wp-admin/update-core.php with a temporary MU-plugin fixture injecting controlled core, plugin, and theme translation updates; verified the rendered translations section shows a count of 3 and entries for WordPress, Hello Dolly, and Twenty Twenty-Four
• PHPUnit execution for Tests_Admin_IncludesUpdate could not be run in this environment because the local WordPress test configuration / Docker test environment was unavailable

Use of AI Tools

AI assistance: Yes
Tool(s): Codex
Model(s): GPT-5-based Codex
Used for: implementation, test scaffolding, server-side smoke-test orchestration, and PR drafting; outputs were reviewed and validated with syntax checks, PHPCS, and an authenticated admin-page smoke test.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

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