react-native-rtl

Flip your React Native app between LTR and RTL at runtime — no restart, no bundle reload, no remount. One call re-mirrors the whole UI and the native chrome (navigation header, native tab bar, and on iOS the edge swipe-back gesture), in place, keeping the user's navigation stack, scroll and form state intact.

The usual I18nManager.forceRTL(true) needs an app restart to take effect. This package doesn't — it rides React Native's own re-layout paths (the ones a cold start uses) to re-lay out every live Fabric surface, and mirrors the native chrome alongside it. No node_modules patch, no navigator swap, no root-key remount.

• Runtime flip — LTR ⇄ RTL without restarting.
• Native New Architecture (Fabric / bridgeless), iOS + Android.
• Autolinked — no MainApplication / Podfile edits.
• Tiny API — setRTL, applyLocaleDirection, isRTLLocale.

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Requirements

• React Native New Architecture (Fabric) — default on RN 0.76+ / Expo SDK 52+.
• A development build or bare app. This is native code, so it does not run in Expo Go — use expo prebuild + expo-dev-client.
• iOS 13+ / Android with android:supportsRtl="true" (the package's manifest merges this in for you; Expo sets it by default).

Installation

npm install react-native-rtl
# or: yarn add react-native-rtl

Rebuild the native app — the JS wrapper is a safe no-op until the native module is in the binary:

# bare React Native
cd ios && pod install && cd ..
npx react-native run-ios && npx react-native run-android

# Expo (development build)
npx expo prebuild
npx expo run:ios && npx expo run:android

Autolinks on both platforms — no manual native edits.

Quick start

import { setRTL, applyLocaleDirection, isRTLLocale } from 'react-native-rtl';

await setRTL(true);   // flip to RTL, instantly
await setRTL(false);  // back to LTR

await applyLocaleDirection('ar'); // RTL (drive it from a locale)
await applyLocaleDirection('en'); // LTR

isRTLLocale('he-IL'); // true

setRTL also keeps JS-side I18nManager.isRTL in sync.

API

Export	Signature	Description
setRTL	(isRTL: boolean) => Promise<boolean>	Flip layout direction at runtime. Resolves to the applied direction. Safe no-op off-device / in Expo Go / tests.
applyLocaleDirection	(locale: string) => Promise<boolean>	setRTL(isRTLLocale(locale)).
isRTLLocale	(locale: string) => boolean	Whether a BCP-47 tag / language code is right-to-left.

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Full integration

Three things to wire up: cold start, the language switch, and (for RTL that follows your text and navigation) a couple of small conventions.

1. Align direction on cold start

Do it before the first screen paints, so a relaunch in the stored language is already correct:

// app root (before rendering your navigator)
const lang = await getStoredLanguage();
await setRTL(isRTLLocale(lang));   // native flip + JS I18nManager
await i18n.changeLanguage(lang);

2. Switch language — direction FIRST, then strings

Call setRTL before i18n.changeLanguage. The tree must be RTL when the new text re-measures; otherwise the new text bakes its alignment while the tree is still LTR.

async function changeLanguage(locale: string) {
  await setRTL(isRTLLocale(locale)); // 1. flip direction (native, no restart)
  await i18n.changeLanguage(locale); // 2. then swap the strings
}

3. Make text follow the direction

React Native only mirrors a <Text> / <TextInput> when its style sets textAlign. Plain unset text stays natural — left on an LTR device, even under forced RTL. Use textAlign: 'left': it is start-relative, so RN keeps it left in LTR and flips it to right under RTL.

const styles = StyleSheet.create({
  title: { fontSize: 20, textAlign: 'left' },   // ✅ flips with direction
  body:  { fontSize: 15 /* no textAlign */ },    // ❌ stays left under RTL
});

Rows built with flexDirection: 'row' reverse automatically under RTL — no change needed.

4. Expo Router / React Navigation — keep animations & gestures in sync

If you use Expo Router (or React Navigation without an explicit direction), the native-stack push/pop animation and the swipe-back gesture read their direction from LocaleDirContext, which defaults to I18nManager.getConstants().isRTL — the cached startup constant. It never updates at runtime, so pushed screens keep the old direction until a restart. Override it with a value that tracks your language state:

import { LocaleDirContext } from '@react-navigation/native';

function RootLayout() {
  const language = useLanguageStore((s) => s.language);
  const direction = isRTLLocale(language) ? 'rtl' : 'ltr';

  return (
    <LocaleDirContext.Provider value={direction}>
      <Stack /* … */ />
    </LocaleDirContext.Provider>
  );
}

(Plain React Navigation: pass direction to NavigationContainer and re-render it on language change instead.)

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How it works

setRTL(isRTL) first keeps JS coherent (I18nManager.allowRTL(true) + forceRTL(isRTL)), then calls the native module, which runs on the main thread in a single pass:

• iOS — flip RCTI18nUtil flags → post UIContentSizeCategoryDidChangeNotification so every RCTFabricSurface stores the new layoutDirection → bust Yoga's size-keyed layout cache by nudging each surface's size 1 pt and restoring it (forces a real re-layout in the new direction) → mirror UINavigationBar / UITabBar semanticContentAttribute and re-arm the interactivePopGestureRecognizer.
• Android — flip I18nUtil flags → forceLayout() + requestLayout() on every ReactSurfaceView (re-runs onMeasure → updateLayoutSpecs → constraintLayout, re-reading isRTL) → set the decor view layoutDirection.

Full deep-dive with exact RN source paths: RTL_RUNTIME_NATIVE.md.

Troubleshooting

Symptom	Cause / fix
Nothing happens at all	Native module not in the binary — rebuild the app (pod install + run). It no-ops in Expo Go.
Only flips after a restart	You're on the New Architecture? Confirm newArchEnabled. Make sure you await setRTL(...) (it re-lays out live surfaces).
Text doesn't right-align	Add textAlign: 'left' to that text style (see step 3). Unset alignment never flips on an LTR device.
Text flips but shows old strings' alignment	Call setRTL before i18n.changeLanguage (step 2).
Push animation / swipe-back keep old direction	Override LocaleDirContext (step 4).

Example

A runnable Expo app lives in example/ — Sufra, a full food-delivery UI (the screen in the GIF above). It shows the flip holding up across a real app: native bottom tabs (expo-router NativeTabs), screens pushed outside the tabs (restaurant detail, a cart modal, checkout, and settings) with native headers, back buttons and the iOS edge swipe-back all mirroring, a shared cart, a @expo/ui SwiftUI control, and English ⇄ Arabic switching that re-mirrors every price, rating and layout in place. See example/README.md.

cd example
npx expo prebuild --clean
npx expo run:ios   # or: npx expo run:android

License

MIT © Saleh Ayman