Phaser I18N

Phaser 4 Internationalization

Overview

No user-facing string is hardcoded in a scene. All player-visible text comes from a typed string catalog keyed by typed constants, so a missing or misspelled key is a compile error and every string has a home for translation. The catalog is a small typed wrapper (no heavy dependency required); locale switching re-renders any open text. Announced strings ([[phaser-accessibility]]) and service messages ([[phaser-services]]) draw from the same catalog.

The typed catalog

One module owns the locales and the lookup. The key type is derived from the default locale so every locale must cover the same keys:

// src/i18n/catalog.ts
const en = {
  "menu.play": "Play",
  "menu.settings": "Settings",
  "hud.score": "Score: {score}",
  "result.cleared": "Level {level} cleared!",
  "lives": "{n} life|{n} lives",     // singular|plural
} as const;

const es: Record<keyof typeof en, string> = {
  "menu.play": "Jugar", "menu.settings": "Ajustes",
  "hud.score": "Puntos: {score}", "result.cleared": "¡Nivel {level} superado!",
  "lives": "{n} vida|{n} vidas",
};

export type StringKey = keyof typeof en;
const locales = { en, es } as const;
export type Locale = keyof typeof locales;

The t() function: interpolation + pluralization

// src/i18n/i18n.ts
let current: Locale = "en";
export function setLocale(l: Locale) { current = l; EventCenter.emit(GameEvent.LocaleChanged); }
export function getLocale() { return current; }

export function t(key: StringKey, params?: Record<string, string | number>): string {
  let s = (locales[current][key] ?? locales.en[key]) as string;   // fall back to en, never crash
  if (s.includes("|") && params && "n" in params)                 // pick plural form
    s = (Number(params.n) === 1 ? s.split("|")[0] : s.split("|")[1]);
  return s.replace(/\{(\w+)\}/g, (_, k) => String(params?.[k] ?? `{${k}}`));
}

Usage is always t(...) with a typed key — never a raw string in a scene:

this.add.bitmapText(x, y, Font.UI, t("hud.score", { score: 0 }));
this.announce(t("result.cleared", { level }));  // [[phaser-accessibility]] live region

The plural/interpolation rules are pure functions — put them in src/logic/** so Vitest covers them ([[phaser-testing]]).

Locale switching at runtime

Changing language must update text that is already on screen. Emit a LocaleChanged event on the EventsCenter ([[phaser-services]]); each scene with visible text subscribes and re-applies t() to its labels, then removes the listener in shutdown (the on/off discipline).

create() {
  const refresh = () => this.scoreText.setText(t("hud.score", { score: this.score }));
  EventCenter.on(GameEvent.LocaleChanged, refresh);
  this.events.once(Phaser.Scenes.Events.SHUTDOWN, () => EventCenter.off(GameEvent.LocaleChanged, refresh));
}

Persist the chosen locale via SaveService and apply it on boot; default from navigator.language when there is no saved choice.

BitmapText vs Text — the localization trade-off

The performance advice "use BitmapText for hot text" (the official game-object-components skill) collides with i18n: a bitmap font only contains the glyphs it was generated with.

• BitmapText — fastest, but the BMFont must include every glyph the locale needs. Fine for digits/Latin HUD; generate per-script font pages ([[phaser-asset-pipeline]]) if you ship CJK/Cyrillic/etc. via BitmapText.
• Text (canvas) — renders any glyph the loaded web font supports, handles diacritics and combining marks, and is the safe choice for arbitrary translated body text and user-generated content. Cost is rasterization per change, so it is for static/low-churn strings.

Rule of thumb: BitmapText for high-churn numeric/short HUD with a covered glyph set; Text for translated prose and any locale whose script the bitmap font does not include. For RTL locales (Arabic/Hebrew), use canvas Text with rtl: true/right alignment and lay out mirrored — BitmapText does not shape RTL.

Project conventions

• Every player-facing string is a t(StringKey, …) call — no inline literals in scenes/entities (this mirrors the no-raw-string-keys discipline).
• The default locale defines the key type; other locales must satisfy it (compile error on a missing key).
• Interpolation/plural logic lives in src/logic/**; the catalog and t() live in src/i18n/**.
• Locale persists via SaveService and is announced through the live region for screen-reader users ([[phaser-accessibility]]).

Verification

Verified by switching locale at runtime and confirming on-screen text updates live (no reload), a missing key fails bun run typecheck, and pluralization unit tests pass for n=0/1/many. For non-Latin locales, confirm glyphs render (no tofu boxes) — that is the signal you need a per-script BMFont page or canvas Text.