# General Translation Platform: isSameDialect
URL: https://generaltranslation.com/en-GB/docs/platform/core/reference/gt-class-methods/locales/is-same-dialect.mdx
---

title: isSameDialect
description: Check whether two locales represent the same dialect. API reference for isSameDialect.

---

Checks whether multiple BCP-47 locale codes represent the same dialect on a [GT](/docs/platform/core/reference/gt-class/constructor) instance. General Translation compares the language and region components of locale codes to determine whether they represent the same linguistic variety.

## Overview [#overview]

Call `isSameDialect` 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 represent the same dialect.

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

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

Signature:

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

*Note: `isSameDialect` runs locally and does not require an API key. Invalid locale codes are handled gracefully and return `false`. For comparisons without a `GT` instance, see the standalone [`isSameDialect`](/docs/platform/core/reference/utility-functions/locales/is-same-dialect).*

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

### Dialect comparison logic

The method determines dialect equality as follows:

1. **Normalise locales** — standardises all input locale codes.
2. **Compare language codes** — all locales must have the same base language.
3. **Handle region hierarchy** — a base language matches its regional variants.
4. **Exact dialect matching** — regional variants must match exactly.

### Hierarchy rules

* A base language (`'en'`) matches any regional variant (`'en-US'`, `'en-GB'`).
* Regional variants match only exactly (`'en-US'` ≠ `'en-GB'`).
* Script variants are considered in the comparison when present.
* Different languages never match (`'en'` ≠ `'es'`).

### Input flexibility

The method accepts:

* Multiple string parameters: `isSameDialect('en-US', 'en-GB')`
* Arrays of strings: `isSameDialect(['en-US', 'en-GB'])`
* Mixed format: `isSameDialect('en-US', ['en-GB', 'en-CA'])`
* A single locale: `isSameDialect('en-US')` (always returns `true`)

## 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 dialect.

## Returns [#returns]

**Type** `boolean`

`true` if all provided locale codes represent the same dialect, `false` otherwise. No exceptions are thrown; invalid locale codes are handled gracefully and return `false`.

## Examples [#examples]

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

// Same exact dialects
console.log(gt.isSameDialect('en-US', 'en-US')); // true
console.log(gt.isSameDialect('zh-CN', 'zh-CN')); // true

// Different dialects of same language
console.log(gt.isSameDialect('en-US', 'en-GB')); // false
console.log(gt.isSameDialect('es-ES', 'es-MX')); // false
console.log(gt.isSameDialect('pt-PT', 'pt-BR')); // false

// Base language with regional variants
console.log(gt.isSameDialect('en', 'en-US')); // true
console.log(gt.isSameDialect('es', 'es-ES')); // true
console.log(gt.isSameDialect('zh', 'zh-CN')); // true

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

## Notes [#notes]

* Uses standardised locale codes for accurate comparison.
* Accepts flexible input formats (strings, arrays, mixed).