Sous-répertoire vs. sous-domaine
This refers to the architectural choice for structuring international websites. A Subdirectory uses folders (e.g., site.com/fr), keeping all authority on one domain. A Subdomain uses prefixes (e.g., fr.site.com), treating each language as a separate "mini-site" in Google's eyes.
The #1 Debate in International SEO
Subdirectories generally rank faster because they share the main site's domain authority—launching site.com/fr immediately inherits years of backlinks and trust signals from site.com. Subdomains start with zero authority and must build reputation independently, as Google treats fr.site.com almost like a completely different domain. However, subdomains are better for distinct, regionally-managed content or when using separate hosting infrastructure. Industry consensus: use subdirectories unless you have a specific technical reason (different platforms, separate teams with full control, regional servers) that requires subdomains.
Subdirectory (/fr) vs. Subdomain (fr.)
Impact dans le monde réel
Brand launches fr.site.com (subdomain) for France
Starts with Domain Authority 1, takes 18 months to rank
Slow growth, limited traffic
Brand uses site.com/fr (subdirectory) instead
Inherits DA 65 from main site, ranks in 2 months
Faster results, higher traffic immediately