Overview

The isSameDialect method checks whether multiple BCP‑47 locale codes represent the same dialect. It compares the language and region components of locale codes to determine whether they represent the same linguistic variety.

Reference

Parameters

Parameter Description

Returns

boolean — true if all provided locale codes represent the same dialect; false otherwise

Throws

No exceptions are thrown. Invalid locale codes are handled gracefully and return false.

Behaviour

Dialect Comparison Logic

The method uses the following logic to determine dialect equality:

1. Normalise locales - Standardises all input locale codes
2. Compare language codes - All locales must share 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

• Base language ('en') matches any regional variant ('en-US', 'en-GB')
• Regional variants only match exactly ('en-US' ≠ 'en-GB')
• Script variants are taken into account 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'])
• Single locale: isSameDialect('en-US') (always returns true)

Examples

Basic Dialect Comparison

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

// Exactly the same dialects
console.log(gt.isSameDialect('en-US', 'en-US')); // true
console.log(gt.isSameDialect('zh-CN', 'zh-CN')); // true

// Different dialects of the 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

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

Next steps

• Compare languages with isSameLanguage
• Check the locale hierarchy with isSupersetLocale
• Validate locales with isValidLocale