# General Translation Platform: standardizeLocale
URL: https://generaltranslation.com/en-GB/docs/platform/core/reference/gt-class-methods/locales/standardize-locale.mdx
---

title: standardizeLocale
description: Normalise a locale code into a standard format. API reference for standardizeLocale.

---

Standardises a BCP-47 locale code to ensure correct formatting and casing on a [GT](/docs/platform/core/reference/gt-class/constructor) instance. General Translation converts locale codes to their canonical form, making them consistent across your application and suitable for use with internationalisation APIs.

## Overview [#overview]

Call `standardizeLocale` on a [`GT`](/docs/platform/core/reference/gt-class/constructor) instance with an optional locale code. When omitted, it uses the instance's `targetLocale`.

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

console.log(gt.standardizeLocale('en-us')); // "en-US"
```

Signature:

```typescript
standardizeLocale(locale?: string): string
```

*Note: `standardizeLocale` runs locally and does not require an API key. It uses the instance's `targetLocale` when `locale` is omitted. For normalisation without a `GT` instance, see the standalone [`standardizeLocale`](/docs/platform/core/reference/utility-functions/locales/standardize-locale).*

## How it works [#how-it-works]

* **Canonicalisation.** Delegates to `Intl.getCanonicalLocales`, which normalises casing: language subtags become lowercase and region subtags become uppercase.
* **Locale fallback.** When `locale` is omitted, the instance's `targetLocale` is used.
* **Passthrough on failure.** Returns the input string unchanged if it cannot be standardised.
* **Missing locale.** Throws an `Error` if no locale is provided and the instance has no `targetLocale` configured.

Common casing corrections applied to hyphenated codes:

* `en-us` → `en-US` (region uppercased)
* `EN-gb` → `en-GB` (language lowercased, region uppercased)
* `fr-ca` → `fr-CA` (proper casing throughout)

## Parameters [#parameters]

| Parameter           | Description                            | Type     | Optional | Default             |
| ------------------- | -------------------------------------- | -------- | -------- | ------------------- |
| [`locale`](#locale) | The BCP-47 locale code to standardise. | `string` | Yes      | `this.targetLocale` |

### `locale` [#locale]

**Type** `string` · **Optional** · **Default** `this.targetLocale`

The BCP-47 locale code to standardise. If not provided, uses the instance's `targetLocale`.

## Returns [#returns]

**Type** `string`

The standardised BCP-47 locale code, or the input string unchanged if it cannot be standardised. Throws an `Error` if no locale is provided and the instance has no `targetLocale` configured.

## Examples [#examples]

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

// Casing is normalised for hyphenated codes
console.log(gt.standardizeLocale('en-us')); // "en-US"
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 [#notes]

* Normalises casing: language codes become lowercase, region codes become uppercase.
* Returns the input string unchanged when the code cannot be standardised.
* Preserves locale extensions and variants when present.