A locale is an identifier representing a combination of language, region, and formatting preferences. Examples include ja-JP (Japanese, Japan), en-US (English, United States), and zh-CN (Chinese, China).

Locales affect every aspect of text display: date formats (2025/01/15 vs 01/15/2025), number formats (1,000 vs 1.000), currency symbols, and sort order. Internationalization programming books explain the locale system.

In JavaScript, the Intl object provides locale-aware formatting. Intl.NumberFormat('ja-JP') produces Japanese-style number formatting.

For multilingual websites, detecting the user's browser locale (navigator.language) and displaying the appropriate language version is standard practice. Web multilingual development books cover implementation patterns.