BCP 47 / IETF Language Tag Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching bcp 47 / ietf language tag, ported and verified for Go. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// BCP 47 / IETF Language Tag
// ReDoS-safe | RegexVault — Localization > Locale & Language

package validation

import "regexp"

var bcp47IetfLanguageTagRe = regexp.MustCompile(`^[a-zA-Z]{2,3}(?:-[a-zA-Z]{4})?(?:-(?:[A-Z]{2}|[0-9]{3}))?$`)

func ValidateBcp47IetfLanguageTag(s string) bool {
    return bcp47IetfLanguageTagRe.MatchString(s)
}

// Example
// fmt.Println(ValidateBcp47IetfLanguageTag("en")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Locale & Language category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Language subtag examples: en=English, zh=Chinese, es=Spanish. Script subtags: Hant=Traditional Chinese, Hans=Simplified Chinese, Latn=Latin. Region subtags: US, CN, TW (ISO 3166-1 alpha-2). Use ISO 639-1 (2-char) or ISO 639-2 (3-char) codes.