ISO 639-1 Language Code Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching iso 639-1 language code, ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// ISO 639-1 Language Code
// ReDoS-safe | RegexVault — Localization > Locale & Language

const iso6391LanguageCodeRegex = /^[a-z]{2}$/;

function validateIso6391LanguageCode(input: string): boolean {
  return iso6391LanguageCodeRegex.test(input);
}

// Example
console.log(validateIso6391LanguageCode("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 JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. 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

ISO 639-1 codes are always lowercase 2 letters. Examples: en=English, zh=Chinese, es=Spanish, ar=Arabic, hi=Hindi, ja=Japanese, ko=Korean. Not all languages have ISO 639-1 codes — use ISO 639-3 (3-char) for less common languages.