Cometchat I18N

Ground truth: the UI Kit CometChatLocalize API + docs/fundamentals. Official docs: https://www.cometchat.com/docs/fundamentals/overview · Docs MCP: claude mcp add --transport http cometchat-docs https://www.cometchat.com/docs/mcp (or fetch the URL directly without MCP). Verify symbols against the installed package/source before relying on them.

Purpose

Localize the CometChat UI Kit to the user's language. Every kit ships with English + ~15 bundled languages (Arabic, Bengali, Chinese, German, Spanish, French, Hindi, Indonesian, Italian, Japanese, Korean, Malay, Portuguese, Russian, Swedish, Turkish — exact set varies by kit version). Custom languages can be added at runtime.

The biggest gotcha: the localization API differs across kits. Web + Angular v5 use CometChatLocalize.init({ ... }) (object); React Native v5 uses a <CometChatI18nProvider> component + useCometChatTranslation hook (no CometChatLocalize.init); Android uses CometChatLocalize.setLocale(context, "es") (Context + code String); iOS uses CometChatLocalize.set(locale: "es"); Flutter has no CometChatLocalize class at all — register the kit's Translations localization delegate. (Angular's positional init("es") was a v4-only form — v5 moved to the object signature, matching React.) This skill is the canonical reference.

API surface per family

React (v6) — object signature

import { CometChatLocalize } from "@cometchat/chat-uikit-react";

CometChatLocalize.init({
  language: "es",
  fallbackLanguage: "en",
});

Object literal. init({ ... }).

React Native (v5) — CometChatI18nProvider (NOT CometChatLocalize.init)

The RN v5 kit does not export a CometChatLocalize class with .init(...) (that was the v4 RN API). v5 localizes through a provider component + a hook. Wrap your app (inside CometChatThemeProvider) and read strings with useCometChatTranslation:

import {
  CometChatThemeProvider,
  CometChatI18nProvider,
} from "@cometchat/chat-uikit-react-native";

const App = () => (
  <CometChatThemeProvider theme={{ mode: "light" }}>
    {/* autoDetectLanguage reads the device locale; or pin one with selectedLanguage="es" */}
    <CometChatI18nProvider autoDetectLanguage={true} fallbackLanguage="en">
      {/* your screens / kit components */}
    </CometChatI18nProvider>
  </CometChatThemeProvider>
);

// In a component:
import { useCometChatTranslation } from "@cometchat/chat-uikit-react-native";
const { t } = useCometChatTranslation();
// t("CHATS")

CometChatI18nProviderProps: selectedLanguage?, autoDetectLanguage?: boolean, fallbackLanguage?, translations?: { [code]: {...} } (verified vs shared/resources/CometChatLocalizeNew/CometChatI18nProvider.tsx). For imperative switching there's setGlobalLanguage(language, translations?, fallback?).

Angular (v5) — OBJECT signature

import { CometChatLocalize } from "@cometchat/chat-uikit-angular";

CometChatLocalize.init({ language: "es" });
// with more options:
CometChatLocalize.init({
  language: "es",
  fallbackLanguage: "en-US",
  timezone: "Europe/Madrid",
});

Object literal, not positional — in v5 (@cometchat/chat-uikit-angular@5), init(settings: LocalizationSettings) takes an object, the same shape as React. (Verified in projects/cometchat-uikit/src/lib/resources/CometChatLocalize/cometchat-localize.ts — static init(settings: LocalizationSettings).) The old positional init("es") form was the v4 Angular API and no longer applies. Switch language at runtime with CometChatLocalize.setCurrentLanguage("fr"), read keys with getLocalizedString(key), and add custom strings with addTranslation({ ... }).

Android V5 — Java/Kotlin static method

// Kotlin — takes (Context, language-code String). Language.* are String constants.
CometChatLocalize.setLocale(context, Language.SPANISH)   // or "es"

// Java
CometChatLocalize.setLocale(context, Language.SPANISH);  // or "es"

setLocale, not init. Signature is setLocale(Context, @Language.Code String) — a Context plus a two-letter language-code String (NOT a java.util.Locale). Language exposes ENGLISH="en", SPANISH="es", FRENCH="fr", GERMAN="de", … (verified vs chatuikit/.../localise/CometChatLocalize.java + Language.kt).

Android V6 (stable) — same as V5

V6 keeps the same API: CometChatLocalize.setLocale(context, "es") (verified vs chatuikit-kotlin/.../localise/CometChatLocalize.kt:22 — fun setLocale(context: Context, language: String)). No drift between V5 and V6.

iOS V5

import CometChatUIKitSwift

CometChatLocalize.set(locale: "es")   // or set(locale: Language.spanish)

The method is set(locale:), not setLocale(...). It takes a String (or a Language) — public class func set(locale: String) / set(locale: Language) (verified vs Components/Shared/Helpers/CometChatLocalize/CometChatLocalize.swift:78,82). There is no setStringResources — override individual strings via your app's Localizable.strings.

Flutter V5 + V6 — there is NO CometChatLocalize.init(...)

Verified against the kit source + docs (ui-kits/cometchat-uikit-flutter-v6, documentation/docs/ui-kit/flutter/localize.mdx): Flutter does NOT expose a CometChatLocalize class. Localization is wired the idiomatic Flutter way — register the kit's Translations localization delegate on your MaterialApp and drive the language through the app's Locale. Earlier drafts of this skill showed CometChatLocalize.init(language: 'es'); that symbol does not exist in the Flutter UI Kit (V5 or V6) — do not emit it.

import 'package:cometchat_chat_uikit/cometchat_chat_uikit.dart' as cc; // V6
// V5: import 'package:cometchat_chat_uikit/cometchat_chat_uikit.dart' as cc; (5.2.x)

MaterialApp(
  // Language follows the app Locale. Set `locale:` to force one, or omit to
  // follow the device + supportedLocales.
  locale: const Locale('es'),
  supportedLocales: const [
    Locale('en'), Locale('ar'), Locale('de'), Locale('es'), Locale('fr'),
    Locale('hi'), Locale('ja'), Locale('ko'), Locale('pt'), Locale('ru'),
    Locale('zh'), // …19 supported total — see the docs list
  ],
  localizationsDelegates: const [
    cc.Translations.delegate,            // ← the CometChat UI Kit strings
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
  ],
  home: const YourHomeScreen(),
);

Read a translated string with cc.Translations.of(context).users. Add a custom language or override one by subclassing cc.Translations and registering your own LocalizationsDelegate before cc.Translations.delegate in the list (full recipe in documentation/docs/ui-kit/flutter/localize.mdx).

Cross-family signature summary

The agent must consult this table before writing any localization code. Verify against the installed package's type definitions if uncertain — the localization surface genuinely differs per family (e.g. React Native moved from a CometChatLocalize class to the <CometChatI18nProvider> component; Flutter never had a CometChatLocalize class).

When to call init/setLocale

After CometChat init is configured but before mounting any kit components:

// React example — in your provider
useEffect(() => {
  CometChatUIKit.init(settings)?.then(() => {
    CometChatLocalize.init({ language: getUserLocale(), fallbackLanguage: "en" });
    // Now mount kit components
  });
}, []);

// Android — in Application.onCreate. setLocale takes (Context, code String).
override fun onCreate() {
  super.onCreate()
  val settings = UIKitSettings.UIKitSettingsBuilder()/* ... */.build()
  CometChatUIKit.init(this, settings, object : CometChat.CallbackListener<String>() {
    override fun onSuccess(p: String) {
      CometChatLocalize.setLocale(this@MyApp, getUserLocale())   // e.g. "es"
    }
    override fun onError(e: CometChatException) {}
  })
}

// iOS — in App.init or AppDelegate. The method is set(locale:), takes a String.
CometChat.init(appId: ...) { _, error in
  guard error == nil else { return }
  let code = Locale.preferredLanguages.first?.split(separator: "-").first.map(String.init) ?? "en"
  CometChatLocalize.set(locale: code)
}

Setting locale before init is harmless but the kit doesn't pick up the locale until init completes; some components read the locale at first render. Doing both in sequence is safest.

Custom languages / overriding strings

Each kit lets you register a custom language or override individual strings.

React / React Native (v6)

CometChatLocalize.init({
  language: "es",
  fallbackLanguage: "en",
  // FLAT key->value map for the ACTIVE language (NOT a nested `resources: { es: {...} }`
  // object — LocalizationSettings has no `resources` field; it's silently ignored).
  translationsForLanguage: {
    "Chat": "Charla",
    "Messages": "Mensajes",
    // ... override only the strings you want, for the active language
  },
});
// To add overrides for additional languages, call CometChatLocalize.addTranslation({...}) per language.

React Native (v5) — translations prop on the provider

<CometChatI18nProvider
  selectedLanguage="es"
  translations={{ es: { CHATS: "Charla", MESSAGES: "Mensajes" } }}
>
  {/* … */}
</CometChatI18nProvider>

Add a brand-new language the same way: translations={{ custom: { CHATS: "…" } }} with selectedLanguage="custom".

Angular

Init with the object signature, then register custom strings via addTranslation (v5):

CometChatLocalize.init({ language: "es" });
CometChatLocalize.addTranslation({
  es: { CHAT: "Charla", MESSAGES: "Mensajes" },
});

Android

The Android kit has no string-override API on CometChatLocalize (no addStringResources/setStringResources). Override individual strings the Android-native way — add a values-es/strings.xml with the kit's string keys to your app resources; Android resource resolution picks them up for the active locale.

CometChatLocalize.setLocale(context, "es")   // selects the locale; string overrides live in res/values-es/

iOS

iOS has no setStringResources API either. Override strings via your app's Localizable.strings (per-locale .lproj) using the kit's string keys; set(locale:) only selects the active locale.

CometChatLocalize.set(locale: "es")   // overrides live in es.lproj/Localizable.strings

Flutter

Flutter has no CometChatLocalize.init — subclass the kit's Translations delegate to override or add strings, and register your delegate before cc.Translations.delegate in MaterialApp.localizationsDelegates (full recipe in documentation/docs/ui-kit/flutter/localize.mdx):

class MyTranslations extends cc.Translations {
  @override
  String get chats => 'Charla';   // override individual getters
}
// register MyTranslationsDelegate() ahead of cc.Translations.delegate

RTL languages

Arabic, Hebrew, Persian, Urdu render right-to-left. The kits handle layout direction automatically based on the locale, BUT:

1. Native iOS / Android: layout direction follows the device's locale OR the explicitly-set CometChat locale, whichever is set last. If your app sets the device locale to Arabic but the kit's locale is English, mismatched RTL is visible.
2. Web (React / Angular): <html dir="rtl"> is required for full RTL support. The kit reads this from the document root. Set it when locale changes:

useEffect(() => {
  const lang = currentLocale;
  document.documentElement.dir = ["ar", "he", "fa", "ur"].includes(lang) ? "rtl" : "ltr";
  CometChatLocalize.init({ language: lang });
}, [currentLocale]);

3. React Native: I18nManager.forceRTL(true) for global RTL flip. Requires app restart to take effect (this is the one common production bug — set RTL, app doesn't visibly change, devs miss the "restart required" warning).

import { I18nManager, NativeModules, Platform } from "react-native";

if (isRTLLocale(language) && !I18nManager.isRTL) {
  I18nManager.forceRTL(true);
  if (__DEV__) {
    console.warn("RTL set — app must restart for layout change to apply");
  } else {
    NativeModules.DevSettings.reload();
  }
}

4. Flutter: handled automatically via MaterialApp.localizationsDelegates + Locale('ar'). Flutter's framework flips layout direction on locale change without restart.

Fallback language

Every kit falls back to English when a translation is missing for the active locale. Make this explicit:

// React/RN/Angular (object signature) — fallbackLanguage is a settings field
CometChatLocalize.init({ language: "es", fallbackLanguage: "en-US" });

Angular v5's LocalizationSettings carries fallbackLanguage (verified in cometchat-localize.ts — defaults to en-US). RN's <CometChatI18nProvider> takes a fallbackLanguage prop. Flutter's Translations delegate and iOS's set(locale:) don't expose an explicit fallback arg — they fall back to English internally, so the skill doesn't try to override it there.

Detecting the user's preferred language

// Web — browser language
const language = navigator.language.split("-")[0];   // "en-US" → "en"

// React Native — device language
import * as Localization from "expo-localization";    // Expo
const language = Localization.locale.split("-")[0];

// or react-native-localize for bare RN:
import { getLocales } from "react-native-localize";
const language = getLocales()[0]?.languageCode ?? "en";

// Android
val language = Locale.getDefault().language          // "en"

// iOS
let language = Locale.preferredLanguages.first?.split(separator: "-").first.map(String.init) ?? "en"

// Flutter
import 'dart:ui';
final language = window.locale.languageCode;          // 'en'

Map these to your kit's locale convention (most kits use ISO 639-1 two-letter codes; Flutter sometimes accepts BCP47 like en-US).

Logout / language switch — re-init the kit

When the user changes language at runtime, simply call init/setLocale again with the new language. The kit re-renders kit components on the next render cycle. No need to logout/re-login.

For React/RN — wrap kit components in a key={language} to force re-mount if the kit doesn't auto-detect:

<div key={language}>
  <CometChatConversations />
</div>

This is the workaround for kits that cache localized strings at first render.

Advanced init options + date/time formatting (web / JS family)

CometChatLocalize.init(settings) (web, RN, Angular) accepts more than a language — the LocalizationSettings carries options the basic recipe omits (all verified in cometchat-uikit-react-v6/src/resources/CometChatLocalize/cometchat-localize.ts):

• translationsForLanguage — inject custom string overrides at init (sugar for addTranslation).
• missingKeyHandler — a callback invoked with any key that has no translation (log it, or return a fallback). Great for catching gaps in custom languages.
• timezone — IANA zone string (e.g. "America/New_York") used when the kit formats timestamps.

Date/time formatting is controlled with CalendarObject (exported from the kit, utils/CalendarObject.ts) — pass one globally or per-component (e.g. a component's lastActiveAtDateTimeFormat-style prop) to control how the kit renders relative/absolute times. Query the docs MCP / ui-kit/react/localize for the full CalendarObject field list and the flag_message_reason_* / message_composer_mention_* translation-key conventions.

These are web/JS-family details. Native families (Android/iOS/Flutter) localize through their own resource/string mechanisms — see the per-family -core/-troubleshooting skills.

Anti-patterns

1. Using the wrong localization surface for the family. Web + Angular v5 take CometChatLocalize.init({ language }) (object); React Native v5 uses <CometChatI18nProvider> + useCometChatTranslation (NO CometChatLocalize.init); Android uses CometChatLocalize.setLocale(context, "es"); iOS uses CometChatLocalize.set(locale: "es"); Flutter has no CometChatLocalize — register the kit's Translations delegate. The legacy positional init("es") only ever applied to Angular v4. Verify against the installed package's types if unsure.
2. Setting locale before kit init. Some kits ignore the early call. Always sequence: kit init → localize init.
3. No fallback language on web/RN/Flutter. Missing translations show as raw keys (CHAT_HEADER_TITLE etc.) instead of English fallback.
4. document.dir not synced with locale on web. RTL languages render LTR — broken layout.
5. I18nManager.forceRTL without app restart. Layout doesn't flip; devs think the kit is broken.
6. Hardcoding language in skill output. Always read user preference (browser/device/explicit setting).
7. Custom resources keyed by lowercase ID ("chat" instead of "CHAT"). Kit string keys are uppercase by convention. Mismatched case = no override applied.
8. Trusting the audit-fix-once mindset. Localize signatures can drift in future minor versions. Re-verify on kit upgrade.

Verification checklist

• init / setLocale signature matches the family in the table above
• Locale set AFTER kit init resolves
• fallbackLanguage set where supported (React, RN, Flutter)
• Web: document.documentElement.dir synced with RTL languages
• React Native: I18nManager.forceRTL warning + restart on RTL set
• Custom resources use uppercase string keys
• Language detection from browser/device, not hardcoded
• Re-init on language switch (or key={language} workaround)
• Smoke test: switch to a bundled non-English language, verify kit components localize
• Smoke test: switch to a missing-resource language, verify English fallback
• RTL smoke test: Arabic / Hebrew on web (with dir="rtl") and RN (with I18nManager.forceRTL) and native Android/iOS — kit components mirror correctly

Pointers

• cometchat-{family}-core — kit init order and conventions (localize hooks into the post-init phase)
• cometchat-{family}-customization — custom string resources / theme strings
• cometchat-{family}-troubleshooting — when localization doesn't apply (cache, sequence, fallback)
• cometchat-a11y — sister skill; localization + accessibility together cover the bulk of "production polish"