Sulu CMS ↔ Symfony Translation: Missing translation fallback behavior

Answer the Question First

In Sulu 3.x the default behaviour is to render an empty string when a field has no translation in the requested locale. From Sulu 4.x the same situation falls back to the master language content. This change is independent of Symfony’s fallbackLocale and only affects Sulu’s own content layer.

SEO & UX Risks

• Master-language fallback (Sulu 4.x)
  • Duplicate content signals if the URL shows a locale that differs from the displayed language.
  • Hreflang tags may point to a page that actually shows master language text, confusing search engines.
  • Users may click through expecting translated content but see the default language, increasing bounce rates.
• Empty-string fallback (Sulu 3.x)
  • Thin content can hurt page relevance and ranking.
  • Missing meta titles/descriptions or image alt text may be omitted, reducing SEO juice.
  • Layouts that rely on content may break or appear incomplete, degrading UX.

Configuration Interaction

The sulu_language_fallback setting defines a fallback chain per webspace and document. It is evaluated by Sulu’s content service before rendering. Symfony’s fallbackLocale is used only for the Symfony Translator component, e.g. messages and validation. Because they operate on separate layers, setting both does not cause a conflict; the Sulu fallback takes precedence for content fields.

Upgrade vs. Custom Override

• Upgrade to Sulu 4.x – the master-fallback behaviour is baked into the core. It simplifies configuration but requires audit of hreflang tags, sitemaps, and user expectations.
• Custom override in Sulu 3.x – you can implement a content event listener that mimics the 4.x fallback, but this adds maintenance overhead and may break with future patch releases.
• Recommendation – If your site relies on strict language separation and you can afford a migration effort, upgrade to Sulu 4.x and adjust hreflang / sitemap logic accordingly. If you need to preserve the empty-string behaviour without upgrading, implement a lightweight override and monitor SEO metrics.

Diagnostic Steps

1. Confirm the active Sulu version: bin/console sulu:version.
2. Check the webspace configuration for sulu_language_fallback in config/packages/sulu_webspace.yaml or the corresponding XML file.
3. Create a test content node with a field translated only in the master language.
4. Request the same node in a secondary locale and inspect the HTML: is the field empty or populated with master content?
5. Verify that Symfony’s fallbackLocale is set in config/packages/translation.yaml and that it does not affect Sulu content rendering.

Next Step

To tailor the recommendation precisely, I need to know which Sulu major version your project is currently running.