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Introduction

Ergonomic application localisation, built on ICU — for JavaScript, PHP, Python, Java, and C#.

As long as you display data, you need to present it in a format your users will understand. Cosmo is a thin, ergonomic layer over ICU: set the locale (language_COUNTRY) and time zone, and your app is ready for its audience — currencies, dates, numbers, units, plurals, collation, and more.

One library, five languages, the same API:

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

const c = new Cosmo("es-ES");
c.money(11000.4, "EUR");     // "11.000,40 €"
c.percentage(0.2);           // "20%"

use Miloun\Cosmo\Cosmo;

$c = new Cosmo('es_ES');
$c->money(11000.4, 'EUR');   // "11.000,40 €"
$c->percentage(0.2);         // "20%"

from cosmo import Cosmo

c = Cosmo("es_ES")
c.money(11000.4, "EUR")      # "11.000,40 €"
c.percentage(0.2)            # "20%"

import com.miloun.cosmo.Cosmo;

Cosmo c = new Cosmo("es_ES");
c.money(11000.4, "EUR");     // "11.000,40 €"
c.percentage(0.2);           // "20%"

using Miloun.Cosmo;

var c = new Cosmo("es-ES");
c.Money(11000.4, "EUR");     // "11.000,40 €"
c.Percentage(0.2);           // "20%"

Pick your language in any code tab — every sample across the whole site switches to match, so you only ever read your own.

Why ICU, and nothing but ICU

Everything comes straight from the runtime's ICU data — it covers every country, language, script, calendar, and time zone. Cosmo bundles no locale data of its own: there are no hardcoded tables to drift out of date. If the runtime's ICU can't produce a result, the feature is omitted, not faked.

The five ports reach ICU through different doors, which is the only reason their feature sets differ at the edges:

Port ICU access Notes
JavaScript the standard Intl API strictly Intl-only; raw-ICU features (RBNF, parsing, transliteration, …) are omitted, not faked
PHP ext-intl (+ raw ResourceBundle, RBNF) the original library; v3 reconstructs the few newer formatters ext-intl lacks from CLDR data
Python PyICU (ICU C++ bindings) the union of PHP and JS, plus the matcher / spoof / parsing family
Java ICU4J (the reference ICU implementation) the most complete port — nothing curated away, nothing left unbound
C# ICU4C (native ICU C library via P/Invoke) near-Java completeness; a few C-API limitations (no AlphabeticIndex, no LocaleMatcher, ICU 72)

See Feature parity for the full method-by-method matrix and Platform notes for what each port can and cannot do.

Next steps