Subdomains or subdirectories: which URL structure should you prefer for a multilingual site?

Why does Google exclude other methods for language separation?

Google's position is clear: URL parameters and detection cookies are not recommended for managing multilingual content. Parameters (example.com?lang=fr) create canonicalization problems and complicate crawling. Google must index multiple variants of the same URL, which dilutes ranking signals.

On the other hand, cookies are invisible to Googlebot during its first pass. The bot cannot determine the language of a page if it displays via browser detection. The result is random indexing, often in the wrong language version, and an inconsistent user experience in the SERPs.

Subdomains vs Subdirectories: what technical difference does it make for Google?

A subdomain (fr.example.com) is technically treated as a semi-autonomous entity. Google assigns it a distinct crawl budget, which can be an advantage if your language versions are large and require intensive independent crawling. However, this also means that domain authority does not automatically transfer: each subdomain must build its own credibility.

A subdirectory (example.com/fr/) directly benefits from the authority of the main domain. All backlinks pointing to example.com also strengthen /fr/, /en/, /de/. Crawling remains unified, simplifying technical management but may create bottlenecks if the site is massive.

Is the hreflang tag really necessary with these structures?

Google does not say “mandatory,” but in practice, hreflang is essential. Without it, even with a clean subdirectory structure, Google cannot guarantee that it will display the correct language version to a French, Spanish, or German user.

Hreflang explicitly indicates: “This page in /fr/ is the French version of /en/ and /de/”. Without this signal, Google relies on contextual clues (language detected in the content, server geo-location, incoming links) that are often insufficient or contradictory. The result is cannibalization between language versions in the SERPs.

• Subdomains and subdirectories are the two structures validated by Google for multilingualism
• URL parameters and cookies create indexing and canonicalization issues
• Hreflang remains essential regardless of the chosen structure to avoid cannibalization between versions
• Subdomains = distinct crawl budget, authority to rebuild; subdirectories = shared authority, unified crawl
• The choice depends on content volume and your international linking strategy

Is this recommendation consistent with real-world observations?

Yes, largely. Multilingual sites using URL parameters systematically encounter indexing problems: duplicate pages, incorrect language served in SERPs, and the need for complex canonical tags that ultimately create more issues than they solve.

However, Google remains deliberately vague on one point: what real impact does the choice of subdomain vs. subdirectory have on ranking? Officially, none. In practice, subdirectories tend to perform better more quickly for new language markets simply because they inherit existing authority. [To be verified]: Google claims to treat subdomains “almost” like directories, but data shows an initial performance gap.

What nuances should be added regarding hreflang?

Google says “use hreflang,” but does not specify that 90% of hreflang implementations contain errors. The most common issues: absence of return tag (if /fr/ points to /en/, /en/ must point to /fr/), incorrect language codes (fr-FR instead of fr), non-canonical URLs in the tags.

Another point that Google omits: hreflang does not guarantee the indexing of all your versions. If your content in /de/ is a word-for-word translation of /en/ without local added value, Google may choose not to index it, hreflang or not. The linguistic signal does not compensate for inter-language duplicate content.

In what cases does this recommendation become insufficient?

For sites managing both language AND country (example: French France vs. French Belgium), Google recommends a combined structure: fr-fr.example.com or example.com/fr-fr/. But this creates exponential complexity. A site with 5 languages and 10 countries = 50 potential versions.

In these cases, the hreflang strategy must be scripted, automated, and continuously audited. A single error on one tag can break the entire chain. Google provides no native tool to massively validate complex hreflang implementations, which is a real problem for enterprise sites.

Which structure should you choose between subdomain and subdirectory?

If you're launching a new language market and your main domain already has authority, prefer subdirectories. You will immediately benefit from existing trust and backlinks. This is the most effective solution to accelerate initial positioning.

If you handle massive content volumes per language (hundreds of thousands of pages), subdomains offer more technical flexibility: distinct geo-located servers, independent content teams, separate crawl budgets. However, you will need to invest in specific linking for each subdomain.

How can you implement hreflang without critical errors?

Use all three methods simultaneously if possible: HTML tags in the head, HTTP headers for PDFs and non-HTML files, and XML sitemap as a safety net. Google crawls all three sources and can correct minor inconsistencies.

Systematically test with Search Console: “International Targeting” section (formerly “Hreflang Tags”). Google reports return errors, missing canonical URLs, invalid language codes. But be careful, Search Console validation is asynchronous: a corrected error can take 2-3 weeks to disappear from the report.

What errors should be absolutely avoided during migration?

Never change structure (subdomain to subdirectory or vice versa) without a comprehensive redirection plan. Google must understand that fr.example.com/page-A has become example.com/fr/page-A. The 301 redirects must point exactly to the linguistic equivalent, not to the homepage of the new subdirectory.

Avoid mixing approaches: if you are using subdirectories for French and English, do not suddenly switch to a subdomain for German “because the local team requests it.” Google may interpret this as a signal of low editorial consistency, which impacts overall trust.

• Audit the current structure: identify any remaining URL parameters or language cookies
• Choose subdomain OR subdirectory based on domain authority and content volume per language
• Implement hreflang in three ways: HTML head, HTTP headers, XML sitemap
• Validate each language via Search Console's international targeting section before going into production
• Set up monitoring alerts to detect hreflang errors post-deployment (tools like OnCrawl, Botify, Screaming Frog)
• Document the logic of the 301 redirect if migrating from URL parameters or other structures