fluent_intl 0.1.1

package:intl formatting backend for fluent_bundle — per-language plural rules and locale-aware number, currency, and date formatting. Zero setup, pure Dart. For Project Fluent.

fluent_intl

The zero-setup formatting backend for fluent_bundle. Add it to a bundle, and Fluent's [one] / [few] / [many] plural cases start matching by each language's real rules, while NUMBER and DATETIME format the local way — digit grouping, currency symbols, the right number of decimal places, date styles — using package:intl.

No initialization, no native code, no assets. Construct IntlBackend() and go. Pure Dart on every platform.

This is a backend — an add-on, not a starting point. Flutter apps start at fluent_flutter; pure Dart starts at fluent_bundle. Of the two backends, this is the lighter default. When you need something package:intl has no option for — measurement units, non-Gregorian calendars, time zones, other digit systems, ordinals for every language — switch to fluent_icu: same .ftl, same calls, one changed line.

Status: 0.x. The API can change between minor versions until 1.0.0 — pre-1.0, the minor is the breaking axis, so pin ^0.N.0 and read the changelog on minor bumps.

like it? a ⭐ star or 👍 like is the entire marketing budget. Bugs & features →

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👀 Peek inside

• Install
• Quick start
• Usage
  • Numbers
  • Currency
  • Dates and times
  • Plurals and ordinals
• Error handling — when an option can't be applied
• Platform support
• Not in the box
• Docs
• License

---

Install

dependencies:
  fluent_intl: ^0.1.1

Nothing else to do, on any platform.

---

Quick start

Same bundle, one extra constructor argument — and the plural rules become real:

import 'package:fluent_intl/fluent_intl.dart';   // re-exports fluent_bundle

final bundle = FluentBundle('en', backend: IntlBackend())..addResource(r'''
items = { $count ->
    [one] { $count } item
   *[other] { $count } items
}
price = { NUMBER($amount, style: "currency", currency: "USD") }
''');

print(bundle.formatMessage('items', args: {'count': 1}));       // "1 item"
print(bundle.formatMessage('items', args: {'count': 5}));       // "5 items"
print(bundle.formatMessage('price', args: {'amount': 1234.5})); // "$1,234.50"

That's the whole integration. Everything else — messages, selectors, markup, fallback, errors — works exactly as it does in fluent_bundle; this package only decides how numbers, dates, and plural categories come out.

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Usage

One group of NUMBER / DATETIME options per section. Every result below is checked by the example test.

Numbers

const ftl = r'''
plain = { NUMBER($n) }
pct = { NUMBER($share, style: "percent") }
compact = { NUMBER($n, notation: "compact") }
sci = { NUMBER($n, notation: "scientific") }
''';

// Same value, three locales — separators, and even the GROUPS, differ:
en.formatMessage('plain', args: {'n': 1234567.89});   // "1,234,567.89"
de.formatMessage('plain', args: {'n': 1234567.89});   // "1.234.567,89"
hi.formatMessage('plain', args: {'n': 1234567.89});   // "12,34,567.89"  ← lakh/crore grouping

// Percent multiplies the value by 100 — pass the fraction, not the percentage:
en.formatMessage('pct', args: {'share': 0.42});       // "42%"

en.formatMessage('compact', args: {'n': 1234000});    // "1.2M"
en.formatMessage('sci', args: {'n': 123456});         // "1E5"

Currency

const ftl = r'''
price = { NUMBER($amount, style: "currency", currency: "USD") }
yen = { NUMBER($amount, style: "currency", currency: "JPY") }
spelled = { NUMBER($amount, style: "currency", currency: "EUR", currencyDisplay: "name") }
''';

en.formatMessage('price', args: {'amount': 1234.5});   // "$1,234.50"

// JPY has zero minor units — no decimals, and no code to write for it:
en.formatMessage('yen', args: {'amount': 1234.5});     // "¥1,235"

// currencyDisplay: "name" spells the currency out:
en.formatMessage('spelled', args: {'amount': 2});      // "2.00 Euro"

Dates and times

const ftl = r'''
styled = { DATETIME($at, dateStyle: "full", timeStyle: "short") }
fields = { DATETIME($at, year: "numeric", month: "long", day: "numeric") }
clock = { DATETIME($at, hour: "numeric", minute: "2-digit", hour12: "false") }
''';
final at = DateTime(2026, 1, 15, 14, 5);

en.formatMessage('styled', args: {'at': at});
// "Thursday, January 15, 2026 2:05 PM"

de.formatMessage('fields', args: {'at': at});   // "15. Januar 2026"
de.formatMessage('clock', args: {'at': at});    // "14:05"

Both styles work: the two presets dateStyle / timeStyle, and the per-field options (year, month, day, hour, minute, …) combined into a custom format.

Plurals and ordinals

The main reason to add a backend — picking the right plural category for Fluent's selectors:

const ftl = r'''
items = { $count ->
    [one] { $count } item
   *[other] { $count } items
}
place = { NUMBER($pos, type: "ordinal") ->
    [one] { $pos }st
    [two] { $pos }nd
    [few] { $pos }rd
   *[other] { $pos }th
}
''';

en.formatMessage('items', args: {'count': 1});   // "1 item"
en.formatMessage('items', args: {'count': 2});   // "2 items"

// type: "ordinal" switches the category rules — "1st, 2nd, 3rd, 4th":
[1, 2, 3, 4].map((n) => en.formatMessage('place', args: {'pos': n}));
// "1st", "2nd", "3rd", "4th"

Cardinal plurals ("1 item" / "5 items") work for every language. Ordinals ("1st, 2nd, 3rd") are this package's own addition — package:intl ships none — so the languages with non-trivial ordinal rules are built in here and tested against the Unicode data. Other languages fall back to the catch-all category; fluent_icu covers every language.

---

Error handling — when an option can't be applied

package:intl has no setting for some options (roundingMode, signDisplay, measurement units, calendars, time zones). This backend never quietly ignores one: it renders the closest form it can and records a FluentTypeError in the error list you pass in.

final en = FluentBundle('en', backend: IntlBackend(), useIsolating: false)
  ..addResource(r'rounded = { NUMBER($n, roundingMode: "floor") }');

final errors = <FluentError>[];
final out = en.formatMessage('rounded', args: {'n': 2.9}, errors: errors);
// out:    "2.9"               ← nearest supported rendering
// errors: [FluentTypeError]   ← the gap, on the record

Users see reasonable output; your tests see every gap. fluent_bundle's test harness checks both directions for every known gap — supported options render with no error, unsupported ones fall back with exactly one. The full per-option list is in Capabilities.

Everything else about errors follows fluent_bundle's rule: failures are values, never thrown.

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Platform support

Pure Dart, no conditional imports, no platform code:

Android	iOS	macOS	Windows	Linux	Web	Servers / CLI
✅	✅	✅	✅	✅	✅	✅

---

Not in the box

What package:intl can't do, this backend can't either — and by design it says so out loud (see above) instead of quietly guessing:

• Measurement units (style: "unit"), non-Gregorian calendars, time zones, numbering systems, signDisplay / roundingMode — fluent_icu renders all of these, on the same FTL.
• Ordinal rules beyond the inlined locales — same answer.
• Message translation workflow (ARB catalogs, extraction) — different job; this package formats, it doesn't manage translations.

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Docs

The README covers the everyday stuff. wanna go deeper?

Doc	What's inside
Architecture	How it's built: the backend, how options map across, where it falls back
Capabilities	Every option, and whether it renders fully, falls back, or isn't supported
Updating	Maintenance recipes and the upstream (intl) watchlist
Example	The whole tour in one runnable file, output checked by test

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License

MIT. See LICENSE.