# General Translation Platform: isSameLanguage
URL: https://generaltranslation.com/en-US/docs/platform/core/reference/gt-class-methods/locales/is-same-language.mdx
Docs index: https://generaltranslation.com/llms.txt
Description: Check whether two locales share the same base language. API reference for isSameLanguage.

Checks whether multiple BCP-47 locale codes represent the same base language, ignoring regional and script differences, on a [GT](/docs/platform/core/reference/gt-class/constructor) instance. General Translation uses this to determine language compatibility and group content by language family.

## Overview [#overview]

Call `isSameLanguage` on a [`GT`](/docs/platform/core/reference/gt-class/constructor) instance with two or more locale codes (or arrays of codes). It returns `true` when they all share the same base language.

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

console.log(gt.isSameLanguage('en-US', 'en-GB')); // true
console.log(gt.isSameLanguage('en-US', 'es-ES')); // false
```

Signature:

```typescript
isSameLanguage(...locales: (string | string[])[]): boolean
```

*Note: `isSameLanguage` runs locally and does not require an API key. For comparisons without a `GT` instance, see the standalone [`isSameLanguage`](/docs/platform/core/reference/utility-functions/locales/is-same-language).*

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

- **Base language comparison.** Compares only the base language code (before the first hyphen).
- **Ignores subtags.** Regional, script, and variant differences are ignored.
- **Variadic input.** Works with a variable number of locale parameters, accepting strings, arrays, or a mix.

## Parameters [#parameters]

| Parameter | Description | Type | Optional | Default |
| --- | --- | --- | --- | --- |
| [`locales`](#locales) | Variable number of locale codes, or arrays of locale codes, to compare. | `(string \| string[])[]` | No | — |

### `...locales` [#locales]

**Type** `(string | string[])[]` · **Required**

A variable number of locale codes (strings) or arrays of locale codes to compare. All provided locales must represent the same base language.

## Returns [#returns]

**Type** `boolean`

`true` if all locale codes represent the same base language, `false` otherwise.

## Examples [#examples]

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

// Same language, different regions
console.log(gt.isSameLanguage('en-US', 'en-GB')); // true
console.log(gt.isSameLanguage('es-ES', 'es-MX')); // true
console.log(gt.isSameLanguage('zh-CN', 'zh-TW')); // true

// Different languages
console.log(gt.isSameLanguage('en-US', 'es-ES')); // false
console.log(gt.isSameLanguage('fr-FR', 'de-DE')); // false

// Base language with variants
console.log(gt.isSameLanguage('en', 'en-US', 'en-GB')); // true
```

## Notes [#notes]

- Compares only the base language code (before the first hyphen).
- Ignores regional, script, and variant differences.
- Essential for language-based content organization.
- Works with a variable number of locale parameters.

## Sitemap

See the full [sitemap](https://generaltranslation.com/sitemap.md) for all pages.