ICU Locale Identifier Regex for Go

What this pattern does

This page provides a well-structured, multi-part regular expression for matching icu locale identifier, 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

// ICU Locale Identifier
// ReDoS-safe | RegexVault — Localization > Locale & Language

package validation

import "regexp"

var icuLocaleIdentifierRe = regexp.MustCompile(`^[a-z]{2,3}(?:_(?:[A-Z]{2}|[0-9]{3})(?:_(?:[A-Z0-9]{2,8}))?)?$`)

func ValidateIcuLocaleIdentifier(s string) bool {
    return icuLocaleIdentifierRe.MatchString(s)
}

// Example
// fmt.Println(ValidateIcuLocaleIdentifier("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

ICU uses underscores as separators (en_US) while BCP 47 uses hyphens (en-US). Java's Locale class uses underscore format. Unicode CLDR supports both via normalization. es_419 is Spanish for Latin America (UN area code 419).