# General Translation Platform: requiresTranslation
URL: https://generaltranslation.com/en-GB/docs/platform/core/reference/gt-class-methods/locales/requires-translation.mdx
---

title: requiresTranslation
description: Check whether translation is needed between two locales. API reference for requiresTranslation.

---

Determines whether translation is needed between a source and target locale on a [GT](/docs/platform/core/reference/gt-class/constructor) instance. General Translation compares locale codes and considers the approved locale list to decide whether content needs to be translated.

## Overview [#overview]

Call `requiresTranslation` on a [`GT`](/docs/platform/core/reference/gt-class/constructor) instance with optional source and target locales. When omitted, it uses the instance's `sourceLocale` and `targetLocale`.

```typescript
const gt = new GT({
  sourceLocale: 'en-US',
  targetLocale: 'es-ES',
  locales: ['en-US', 'es-ES', 'fr-FR', 'de-DE'],
});

console.log(gt.requiresTranslation('en-US', 'es-ES')); // true
console.log(gt.requiresTranslation('en', 'en-US')); // false (same dialect)
```

Signature:

```typescript
requiresTranslation(
  sourceLocale?: string,
  targetLocale?: string,
  approvedLocales?: string[],
  customMapping?: CustomMapping
): boolean
```

*Note: `requiresTranslation` runs locally and does not require an API key. When arguments are omitted, it uses the instance's `sourceLocale`, `targetLocale`, `locales`, and `customMapping`. For checks without a `GT` instance, see the standalone [`requiresTranslation`](/docs/platform/core/reference/utility-functions/locales/requires-translation).*

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

The method resolves in this order:

1. **Validity.** If the source, target, or any approved locale is not a valid locale, returns `false`.
2. **Same dialect.** If the source and target are the same dialect (for example, `en` and `en-US`), returns `false` — no translation is needed.
3. **No approved list.** If no `approvedLocales` apply, returns `true` when the source and target differ.
4. **Approved scope.** Otherwise, returns `true` only if the target language matches the language of at least one approved locale; different dialects of the same language are treated as requiring translation (so a closer dialect can serve as a fallback). If the target language is not represented in the approved locales, returns `false`.

When `sourceLocale` or `targetLocale` is omitted, the instance's values are used. Throws an `Error` if no source locale is provided and the instance has no `sourceLocale`, or if no target locale is provided and the instance has no `targetLocale`.

## Parameters [#parameters]

| Parameter                              | Description                           | Type                                                                  | Optional | Default              |
| -------------------------------------- | ------------------------------------- | --------------------------------------------------------------------- | -------- | -------------------- |
| [`sourceLocale`](#source-locale)       | The source locale code.               | `string`                                                              | Yes      | `this.sourceLocale`  |
| [`targetLocale`](#target-locale)       | The target locale code.               | `string`                                                              | Yes      | `this.targetLocale`  |
| [`approvedLocales`](#approved-locales) | Array of approved target locales.     | `string[]`                                                            | Yes      | `this.locales`       |
| [`customMapping`](#custom-mapping)     | Custom mapping for locale resolution. | [`CustomMapping`](/docs/platform/core/reference/types/custom-mapping) | Yes      | `this.customMapping` |

### `sourceLocale` [#source-locale]

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

The source locale code. If not provided, the instance's `sourceLocale` is used.

### `targetLocale` [#target-locale]

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

The target locale code. If not provided, the instance's `targetLocale` is used.

### `approvedLocales` [#approved-locales]

**Type** `string[]` · **Optional** · **Default** `this.locales`

Array of approved target locales. If not provided, uses the instance's `locales` array. When the target locale is not in this list, the method returns `false`.

### `customMapping` [#custom-mapping]

**Type** [`CustomMapping`](/docs/platform/core/reference/types/custom-mapping) · **Optional** · **Default** `this.customMapping`

Custom mapping for locale resolution.

## Returns [#returns]

**Type** `boolean`

`true` if translation is required, `false` otherwise. Throws an `Error` if no source or target locale can be resolved.

## Examples [#examples]

```typescript
const gt = new GT({
  sourceLocale: 'en-US',
  targetLocale: 'es-ES',
  locales: ['en-US', 'es-ES', 'fr-FR', 'de-DE'],
});

// Different languages require translation
console.log(gt.requiresTranslation('en-US', 'es-ES')); // true
console.log(gt.requiresTranslation('en-US', 'fr-FR')); // true

// Exact same dialect does not require translation
console.log(gt.requiresTranslation('en-US', 'en-US')); // false
console.log(gt.requiresTranslation('es-ES', 'es-ES')); // false
console.log(gt.requiresTranslation('en', 'en-US')); // false (same dialect)

// Different dialects of the same language DO require translation
// (a closer dialect can serve as a fallback)
console.log(gt.requiresTranslation('en-US', 'en-GB')); // true
console.log(gt.requiresTranslation('es-ES', 'es-MX')); // true

// Target language not represented in approved locales
console.log(gt.requiresTranslation('en-US', 'it-IT')); // false (it-IT not in approved locales)
```

## Notes [#notes]

* Returns `false` only for the exact same dialect, invalid locales, or a target whose language is not represented in the approved locales.
* Different dialects of the same language (for example, `en-US` and `en-GB`) require translation, so a closer dialect can serve as a fallback.
* Respects the approved locale list: matching is by language, not exact dialect.