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Getting started

Requirements

  • Node 20+ (Node 22+ for duration(), which uses Intl.DurationFormat).
  • A modern browser works too — everything is built on the standard Intl API.
  • PHP 8.4+ with the intl extension (php -m | grep intl).
  • Python 3.9+ and the system ICU development libraries (e.g. libicu-dev on Debian/Ubuntu, icu4c on macOS). PyICU is installed as a dependency.
  • Java 11+. ICU4J (com.ibm.icu:icu4j) is pulled in transitively — it bundles its own ICU data, so there is no system library to install.
  • .NET 8+. The NuGet package bundles the ICU4C native libraries, so there is no system-level ICU to install.

Install

npm install @miloun/cosmo

composer require salarmehr/cosmopolitan

Package name vs namespace

For a smooth v2 → v3 upgrade the Composer package keeps its long-standing name salarmehr/cosmopolitan; only the namespace rebrands to Miloun\Cosmo. Existing users bump the constraint to ^3.0 and run a Salarmehr\Cosmopolitan → Miloun\Cosmo find/replace.

pip install cosmo-intl

The distribution is cosmo-intl; the import name is cosmo (from cosmo import Cosmo), decoupled like beautifulsoup4 → bs4.

<dependency>
  <groupId>com.miloun</groupId>
  <artifactId>cosmo</artifactId>
  <version>1.0.0</version>
</dependency>

Gradle: implementation("com.miloun:cosmo:1.0.0").

dotnet add package Miloun.Cosmo

Quick start

Construct with a locale (and an optional time zone, calendar, or currency modifier), then call methods on it. New to these codes? See Locales & time zones.

import { Cosmo } from "@miloun/cosmo";

const c = new Cosmo("en-AU", { timeZone: "Australia/Sydney" });

c.country();            // "Australia"
c.money(1234.5, "AUD"); // "$1,234.50"  (JS needs an explicit currency)
c.number(1234567.89);   // "1,234,567.89"
c.flag();               // "🇦🇺"

use Miloun\Cosmo\Cosmo;

$c = new Cosmo('en_AU', ['timeZone' => 'Australia/Sydney']);

$c->country();          // "Australia"
$c->money(1234.5);      // "$1,234.50"  (currency inferred from region)
$c->number(1234567.89); // "1,234,567.89"
$c->flag();             // "🇦🇺"

PHP 8.4 lets you call a method directly on new Cosmo(...) without wrapping parentheses, or use the cosmo() helper: cosmo('en_AU')->country().

from cosmo import Cosmo

c = Cosmo("en_AU", {"timeZone": "Australia/Sydney"})

c.country()             # "Australia"
c.money(1234.5)         # "$1,234.50"  (currency inferred from region)
c.number(1234567.89)    # "1,234,567.89"
c.flag()                # "🇦🇺"

import com.miloun.cosmo.Cosmo;
import com.miloun.cosmo.Modifiers;

// Modifiers(calendar, currency, timeZone) — any field may be null.
Cosmo c = new Cosmo("en_AU", new Modifiers(null, null, "Australia/Sydney"));

c.country();            // "Australia"
c.money(1234.5);        // "$1,234.50"  (currency inferred from region)
c.number(1234567.89);   // "1,234,567.89"
c.flag();               // "🇦🇺"

using Miloun.Cosmo;

// Modifiers(calendar, currency, timeZone) — any field may be null.
var c = new Cosmo("en-AU", new Modifiers(timeZone: "Australia/Sydney"));

c.Country();            // "Australia"
c.Money(1234.5);        // "$1,234.50"  (currency inferred from region)
c.Number(1234567.89);   // "1,234,567.89"
c.Flag();               // "🇦🇺"

Locale format

Underscore locales (en_AU) and BCP-47 tags (en-AU), including Unicode extensions like fa-IR-u-nu-latn-ca-buddhist, are all accepted. JavaScript prefers the hyphenated form; PHP, Python, Java, and C# accept either. See Locales & time zones for the format explained and how to find yours.

Constructing without a string

Both factory helpers exist in every port (snake_case in Python; typed Subtags/Modifiers value classes in Java and C#):

Cosmo.fromSubtags({ language: "en", region: "AU" });
Cosmo.fromAcceptLanguage(req.headers["accept-language"]);

Cosmo::fromSubtags(['language' => 'en', 'region' => 'AU']);
Cosmo::fromAcceptLanguage($_SERVER['HTTP_ACCEPT_LANGUAGE']);

Cosmo.from_subtags({"language": "en", "region": "AU"})
Cosmo.from_accept_language(request.headers["accept-language"])

// Subtags(language, script, region)
Cosmo.fromSubtags(new Subtags("en", null, "AU"));
Cosmo.fromAcceptLanguage(request.getHeader("Accept-Language"));

// Java adds a CLDR-negotiating overload against your supported locales:
Cosmo.fromAcceptLanguage(header, List.of("en-GB", "fr-FR", "de-DE"));

// Subtags(language, script, region)
Cosmo.FromSubtags(new Subtags("en", "", "AU"));
Cosmo.FromAcceptLanguage(request.Headers["Accept-Language"]);

Negotiating against your own locales

Python and Java can pick the best of your supported locales for a user (CLDR language distance, not prefix matching) — see Negotiation & names.

Ready for the details? Head to the Guide.