Free localization developer tool

Free online locale code converter

Enter a locale such as en_US, pt-BR, zh-Hant-TW, or a common language name. Get canonical codes and readable details instantly.

Try en_US, pt-BR, zh-Hant-TW, Serbian, or Brazilian Portuguese.

American English

Canonical BCP 47
en-US
POSIX / underscore
en_US
Language
en — English
Script
Not specified
Region
US — United States
Likely maximized locale
en-Latn-US
Writing direction
Left to right

Private by design. This tool runs entirely in your browser. Pasted values are never stored or included in analytics, and only the result leaves your browser, when you ask us to email it to you as a PDF.

Hreflang Tag GeneratorPaste one language code and absolute URL per line. The generator validates the set and creates reciprocal-ready HTML link tags.i18n JSON Key CheckerPaste a source-language JSON dictionary and a target translation. Find missing and extra nested keys instantly without uploading either file.

How to use the locale code converter

  1. Enter a locale identifierType a BCP 47 tag, POSIX-style locale, or language name in the input field.
  2. Review the canonical formatsCheck the normalized BCP 47 and underscore forms plus the detected language, script, region, and writing direction.
  3. Copy the conversionCopy the labeled result when you are ready to use the locale in code or configuration.

Convert locale formats without guessing

Locale identifiers look small, but inconsistent casing, separators, and region assumptions regularly break language routing and translation fallbacks. This converter canonicalizes a code with the browser Internationalization API and shows the equivalent formats side by side.

You can start with a BCP 47 tag, an underscore-style code, or a common language name. The result separates the language, script, and region so you can see exactly what the identifier promises to users and software.

BCP 47, POSIX, and ISO codes explained

BCP 47 is the web standard: language first, then optional script and region subtags separated by hyphens. POSIX-style locales commonly use underscores. The language subtag normally comes from ISO 639, while the two-letter region subtag comes from ISO 3166-1.

Canonicalization fixes presentation, not meaning. For example, it can normalize casing and known aliases, but it cannot decide whether generic Spanish should become es-ES or es-MX. That product decision should reflect the content you actually translated.

Use the narrowest locale that stays accurate

Choose a language-only tag when one translation genuinely serves every region. Add a region when spelling, currency, legal text, measurements, or product availability differs. Add a script when readers of the same language use materially different writing systems.

Everything entered here is processed in your browser. Multilocale never stores the value or attaches it to analytics events, and receives the conversion only when you ask us to email it to you as a PDF.

Frequently asked questions

What is the difference between en-US and en_US?

en-US is the BCP 47 form used by HTML, hreflang, JavaScript, and most web APIs. en_US is the POSIX-style form still used by some operating systems, databases, and translation files. They usually describe the same English-for-the-United-States locale.

Is a locale code the same as a language code?

No. A language code such as en identifies a language. A locale can also identify a script, region, or both, such as zh-Hant-TW for Traditional Chinese used in Taiwan. Use only the detail your product actually needs.

Which locale format should I use on the web?

Use canonical BCP 47 tags with hyphens for HTML lang attributes, hreflang, Intl APIs, and HTTP language negotiation. Keep underscore codes only when an existing framework or file convention explicitly requires them.