Seo
Jul 11, 2026
Hreflang Tags With Underscores Are Silently Ignored — ISO Code Syntax, Bidirectional Links, and Implementation Methods
Hreflang tags with underscores (en_GB instead of en-GB), lowercase region codes (en-gb), or uppercase language codes (EN-GB) are silently ignored by Google with no error message. Here's the ISO 639-1 and ISO 3166-1 case requirements, why self-referential tags and bidirectional return links are both required, the three implementation methods and why mixing them breaks the cluster, and when country-targeting without language differences works.