[P2] Audit: Hreflang and canonical consistency needs automated validation

[baixiangcpp]

Imported from the byteflow.tools deep audit on 2026-06-22.

Problem: the site supports multiple locales. Manual checks showed locale pages are reachable, but hreflang and canonical consistency should be automatically validated across all locales and page types.

Affected locales:

• en, zh-CN, zh-TW, ja, ko, de, fr

Affected page types:

• Home pages
• Category pages
• Tool pages
• Workflow pages
• Cluster/tutorial pages
• Legal and PWA pages

Reproduction steps:

1. Select representative URLs in each locale.
2. Inspect canonical tags.
3. Inspect hreflang alternates and x-default.
4. Verify each alternate points to the corresponding localized page.
5. Verify reciprocal links exist from every locale.

Expected behavior: every localized canonical page should self-canonicalize and include reciprocal hreflang tags for all available locales plus x-default where appropriate.

Actual behavior: localization appears broad, but no automated guarantee was found.

Impact: wrong-language ranking, duplicate locale indexation, and weaker international SEO.

Proposed fix:

• Add a hreflang/canonical validation script.
• Generate alternates from route manifest data.
• Fail builds when any locale URL lacks a reciprocal alternate.
• Verify x-default behavior for root route.
• Add tests for locale canonical tags.

Acceptance criteria:

• Every indexable localized page has correct self-canonical.
• Hreflang alternates are reciprocal.
• x-default points to the intended root or language selector.
• CI catches missing or mismatched alternates.

[baixiangcpp]

Closed as completed by the canonical BF audit backlog work. This older non-BF audit issue duplicates work now merged through PRs #209-#219, with the BF issues closed and guard/test coverage in place. The remaining non-duplicate follow-up is #7, which stays open because the upstream Next/PostCSS advisory is not fixed yet.