# generaltranslation: General Translation Core SDK: standardizeLocale
URL: https://generaltranslation.com/en-GB/docs/core/class/methods/locales/standardize-locale.mdx
---
title: standardizeLocale
description: API reference for the GT standardizeLocale method
---

## Overview

The `standardizeLocale` method standardises a BCP-47 locale code to ensure correct formatting and casing.
It converts locale codes to their proper canonical format, making them suitable for use with internationalisation APIs and ensuring consistency across your application.

***

## Reference

### Parameters

<TypeTable
  type={{
  "locale?": {
    type: 'string',
    optional: true,
    default: 'this.targetLocale'
  }
}}
/>

### Parameter descriptions

| Parameter | Description                                                                                       |
| --------- | ------------------------------------------------------------------------------------------------- |
| `locale`  | The BCP-47 locale code to standardise. If not provided, the instance&#39;s `targetLocale` is used |

### Returns

`string` - The standardised BCP-47 locale code, or an empty string if the input is invalid

### Throws

* `Error` - If no locale is provided and the instance has no `targetLocale` configured

***

## Behaviour

Common format corrections applied:

* `en_US` → `en-US` (underscore to hyphen)
* `zh_cn` → `zh-CN` (underscore to hyphen, casing)
* `EN-gb` → `en-GB` (language lowercase, region uppercase)
* `Fr-ca` → `fr-CA` (proper casing throughout)
* `ja_jp` → `ja-JP` (underscore and casing)

***

## Examples

```typescript
const gt = new GT({
  sourceLocale: 'en',
  targetLocale: 'es-ES'
});

// Standardise various locale formats
console.log(gt.standardizeLocale('en_us')); // "en-US"
console.log(gt.standardizeLocale('zh_cn')); // "zh-CN"
console.log(gt.standardizeLocale('EN-gb')); // "en-GB"
console.log(gt.standardizeLocale('fr-ca')); // "fr-CA"

// Already standardised locales pass through unchanged
console.log(gt.standardizeLocale('es-ES')); // "es-ES"
console.log(gt.standardizeLocale('ja-JP')); // "ja-JP"
```

***


## Notes

* Converts underscores to hyphens and normalises casing
* Returns an empty string for invalid locale codes
* Language codes become lowercase, region codes become uppercase
* Preserves locale extensions and variants when present

## Next steps

* Validate standardised locales with [`isValidLocale`](/docs/core/class/methods/locales/is-valid-locale)
* Resolve canonical locales with [`resolveCanonicalLocale`](/docs/core/class/methods/locales/resolve-canonical-locale)
* Get locale properties with [`getLocaleProperties`](/docs/core/class/methods/locales/get-locale-properties)