ngx-fluent

An Angular library for Fluent.

Angular compatibility

Latest version available for each version of Angular

@apappas1129/ngx-fluent	Angular	@fluent/bundle
>= 1.0	13.x	< 1.x
>= 1.1	14.x	< 1.x
>= 1.2	15.x	< 1.x
>= 2.0	16.x	< 1.x
>= 3.0	17.x	< 1.x
>= 4.0	18.x	< 1.x
>= 19.0	19.x	< 1.x
>= 20.0	20.x	< 1.x
>= 21.0	21.x	< 1.x
>= 22.0	22.x	< 1.x

Installation

npm install --save @fluent/bundle @apappas1129/ngx-fluent

---

Setup — standalone apps (recommended)

For any Angular project using standalone bootstrap (bootstrapApplication).

1. Register the library

Add provideHttpClient() and provideNgxFluent() to your ApplicationConfig. Specify defaultLocale to have the translation file fetched before the root component renders — no flash of untranslated keys on first paint:

// app.config.ts
import { ApplicationConfig, provideBrowserGlobalErrorListeners } from '@angular/core';
import { provideHttpClient } from '@angular/common/http';
import { provideNgxFluent } from '@apappas1129/ngx-fluent';

export const appConfig: ApplicationConfig = {
  providers: [
    provideBrowserGlobalErrorListeners(),
    provideHttpClient(),
    provideNgxFluent({
      sources: {
        en: 'assets/i18n/en.ftl',
        sv: 'assets/i18n/sv.ftl',
      },
      defaultLocale: 'en',
    }),
  ],
};

provideHttpClient() is a required prerequisite. The library uses Angular's HttpClient to fetch .ftl files but intentionally does not register it internally, so your app retains full control over interceptors and fetch configuration.

2. Use the pipe

Import NgxFluentPipe in any standalone component that needs translations:

import { NgxFluentPipe } from '@apappas1129/ngx-fluent';

@Component({
  imports: [NgxFluentPipe],
  template: `
    <h1>{{ 'welcome-user' | fluent: { user: name } }}</h1>
  `,
})
export class MyComponent {
  name = 'John Doe';
}

The pipe returns the key as-is if the translation cannot be resolved (locale not loaded, key missing).

3. Deferred locale init from user preference

Omit defaultLocale if you want to decide the initial locale at runtime — for example, from a value stored in localStorage:

// app.config.ts — no defaultLocale
provideNgxFluent({
  sources: {
    en: 'assets/i18n/en.ftl',
    sv: 'assets/i18n/sv.ftl',
  },
}),

// app.ts — set locale after app starts
export class App {
  private fluent = inject(NgxFluentService);

  constructor() {
    const saved = localStorage.getItem('locale') ?? 'en';
    this.fluent.setLocale(saved);
  }
}

The root component renders before the first locale loads, so untranslated keys will briefly appear. Prefer defaultLocale when a hard-coded startup locale is acceptable.

---

Setup — NgModule apps (legacy)

For projects that still bootstrap with platformBrowserDynamic().bootstrapModule(AppModule). This pattern is fully supported; the library ships NgxFluentModule specifically for this case.

1. Register the library

Import NgxFluentModule into your root AppModule. It registers HttpClient internally with DI-based interceptor support, so no separate HttpClientModule is needed:

// app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { NgxFluentModule } from '@apappas1129/ngx-fluent';

@NgModule({
  imports: [
    BrowserModule,
    NgxFluentModule,
  ],
  bootstrap: [AppComponent],
})
export class AppModule {}

2. Configure sources in your root component

Inject NgxFluentService and configure it in ngOnInit. Translated content appears after the first ngOnInit cycle rather than on first paint (unlike the standalone defaultLocale path):

// app.component.ts
import { Component, OnInit } from '@angular/core';
import { NgxFluentService } from '@apappas1129/ngx-fluent';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
})
export class AppComponent implements OnInit {
  constructor(private fluent: NgxFluentService) {}

  ngOnInit() {
    this.fluent.setTranslationSourceMap({
      en: 'assets/i18n/en.ftl',
      sv: 'assets/i18n/sv.ftl',
    });
    this.fluent.setLocale('en');
  }
}

3. Use the pipe

NgxFluentModule exports the fluent pipe, making it available in all components declared in your AppModule — no per-component import needed:

<h1>{{ 'welcome-user' | fluent: { user: name } }}</h1>

The pipe returns the key as-is if the translation cannot be resolved.

---

Translation source formats

Each locale key in sources (or passed to setTranslationSourceMap()) accepts one of three formats:

URL string — the library fetches the file and builds the bundle automatically:

sources: {
  en: 'assets/i18n/en.ftl',
}

URL with bundle options — same fetch, but you control the FluentBundle constructor config (e.g. disable Unicode isolation markers):

sources: {
  en: {
    path: 'assets/i18n/en.ftl',
    bundleConfig: {
      useIsolating: false,
    },
  },
}

Pre-built FluentBundle instance — hand the library a bundle you constructed yourself. No HTTP fetch is performed:

import { FluentBundle, FluentResource } from '@fluent/bundle';

const bundle = new FluentBundle('en', { useIsolating: false });
bundle.addResource(new FluentResource('welcome-user = Welcome, {$user}!'));

sources: {
  en: bundle,
}

This gives you full control — useful for testing, SSR, or bundling translations at build time.

Tip: Make your locale keys compliant to the BCP 47 standard to avoid issues with Fluent's built-in functions that rely on the Intl API.

---

Adding locales incrementally

Sources don't have to be declared all at once. Call setTranslationSourceMap() at any point to register additional locales — for example, when the user opens a language picker for the first time:

// On startup, register only the default
this.fluent.setTranslationSourceMap({ en: 'assets/i18n/en.ftl' });
this.fluent.setLocale('en');

// Later, register more on demand
this.fluent.setTranslationSourceMap({ sv: 'assets/i18n/sv.ftl', fr: 'assets/i18n/fr.ftl' });

Passing a locale key that is already loaded causes its translations to be reloaded from the new source.

---

Switching locale

Call setLocale() on NgxFluentService at any time. The service fetches the translation file if not already cached, then all active fluent pipes update reactively:

// standalone
private fluent = inject(NgxFluentService);

// NgModule
constructor(private fluent: NgxFluentService) {}

// both
this.fluent.setLocale('sv');

Switching to a previously loaded locale is instantaneous — files are cached in memory after the first fetch.

---

Translating programmatically

translate() is synchronous and reads directly from the currently loaded bundle:

// standalone
private fluent = inject(NgxFluentService);

// NgModule
constructor(private fluent: NgxFluentService) {}

// both
getLabel(key: string) {
  return this.fluent.translate(key, { user: 'John' }) ?? key;
}

Returns null if the locale is not loaded or the key is not found. The ?? key fallback mirrors what the pipe does automatically.

---

Example projects

This repository ships two example projects.

ngx-fluent-example-standalone — a modern Angular 22 standalone app. Zoneless (no zone.js), signal-based component state, OnPush change detection by default, provideNgxFluent in app.config.ts. Reference implementation for new projects consuming the library today.

ngx-fluent-example — an Angular 22 project intentionally structured with AppModule and platformBrowserDynamic bootstrap. For teams that cannot yet migrate to standalone — demonstrates that NgxFluentModule provides the same behavior under the NgModule pattern. Retains zone.js, ChangeDetectionStrategy.Eager, and constructor injection, all of which are correct for that pattern.

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Contributing

See Contributing Guide.