Internationalization Support in Node.js with ICU

1. Internationalization Features in Node.js

• Unicode-aware functions like String.prototype.normalize(), toLowerCase(), and toUpperCase().
• The Intl object and locale-sensitive methods such as localeCompare() and Date.prototype.toLocaleString().
• IDN support in the WHATWG URL parser.
• Utilities like buffer.transcode() and util.TextDecoder.
• Support for RegExp Unicode Property Escapes.

2. Build Options for ICU

Four main options control ICU usage when compiling Node.js:

• none: Disables ICU; most internationalization features are unavailable.
• system-icu: Links against ICU installed on the system. Support depends on available locale data.
• small-icu: Embeds limited ICU data (usually English-only) in the binary.
• full-icu: Embeds the full ICU dataset. Default in official Node.js binaries.

3. Feature Comparison

Feature	none	system-icu	small-icu	full-icu
normalize()	disabled	full	full	full
Intl	disabled	partial/full	partial (English-only)	full
localeCompare()	not locale-aware	full	full	full
Date.toLocaleString()	not locale-aware	partial/full	partial (English-only)	full
TextDecoder	basic	partial/full	Unicode-only	full
RegExp Unicode	disabled	full	full	full

4. Providing ICU Data at Runtime

With small-icu, additional ICU data can be loaded at runtime:

• Using the --icu-data-dir CLI option.
• Setting the NODE_ICU_DATA environment variable.
• Configuring --with-icu-default-data-dir at build time.

The full-icu npm module simplifies installation by downloading the correct ICU dataset for the running Node.js version.

5. Detecting ICU Support

• typeof Intl === 'object': Checks if Intl is available.
• typeof process.versions.icu === 'string': Confirms ICU is enabled.
• Testing Intl.DateTimeFormat with non-English locales verifies full ICU support.

6. Example

const january = new Date(9e8);
const spanish = new Intl.DateTimeFormat('es', { month: 'long' });
console.log(spanish.format(january)); // "enero" with full-icu

Conclusion

Internationalization support in Node.js, powered by ICU, enables developers to build multilingual and locale-sensitive applications. Depending on project needs, developers can choose between none, system-icu, small-icu, or full-icu. Full-icu provides the richest feature set, while small-icu balances binary size with basic functionality.