auto-detect composer language from keyboard

adds a new expo-keyboard-language native module that reads the current
keyboard language on iOS (via first responder's textInputMode) and
Android (via InputMethodManager). iOS also gets real-time updates when
the keyboard language changes.

users opt in via Settings > Languages > "Automatically detect post
language from keyboard" (native only, marked experimental). when
enabled, the composer language tracks the keyboard language. users can
override per-session by selecting a language manually, and re-enable
auto mode via the "Automatic" item in the language menu.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

modules/expo-keyboard-language/android/build.gradle

@@ -0,0 +1,39 @@
+apply plugin: 'com.android.library'
+
+group = 'expo.modules.keyboardlanguage'
+version = '1.0.0'
+
+def expoModulesCorePlugin = new File(project(":expo-modules-core").projectDir.absolutePath, "ExpoModulesCorePlugin.gradle")
+apply from: expoModulesCorePlugin
+applyKotlinExpoModulesCorePlugin()
+useCoreDependencies()
+useExpoPublishing()
+
+def useManagedAndroidSdkVersions = false
+if (useManagedAndroidSdkVersions) {
+  useDefaultAndroidSdkVersions()
+} else {
+  buildscript {
+    ext.safeExtGet = { prop, fallback ->
+      rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
+    }
+  }
+  project.android {
+    compileSdkVersion safeExtGet("compileSdkVersion", 34)
+    defaultConfig {
+      minSdkVersion safeExtGet("minSdkVersion", 21)
+      targetSdkVersion safeExtGet("targetSdkVersion", 34)
+    }
+  }
+}
+
+android {
+  namespace "expo.modules.keyboardlanguage"
+  defaultConfig {
+    versionCode 1
+    versionName "1.0.0"
+  }
+  lintOptions {
+    abortOnError false
+  }
+}

modules/expo-keyboard-language/android/src/main/java/expo/modules/keyboardlanguage/ExpoKeyboardLanguageModule.kt

@@ -0,0 +1,31 @@
+package expo.modules.keyboardlanguage
+
+import android.os.Build
+import android.view.inputmethod.InputMethodManager
+import androidx.core.content.getSystemService
+import expo.modules.kotlin.modules.Module
+import expo.modules.kotlin.modules.ModuleDefinition
+
+class ExpoKeyboardLanguageModule : Module() {
+  override fun definition() =
+    ModuleDefinition {
+      Name("ExpoKeyboardLanguage")
+
+      Function("getCurrentKeyboardLanguage") {
+        val context = appContext.reactContext ?: return@Function null
+        val imm = context.getSystemService<InputMethodManager>() ?: return@Function null
+        val subtype = imm.currentInputMethodSubtype ?: return@Function null
+
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+          val tag = subtype.languageTag
+          if (tag.isNotEmpty()) return@Function tag
+        }
+
+        @Suppress("DEPRECATION")
+        val locale = subtype.locale
+        if (locale.isNotEmpty()) return@Function locale
+
+        return@Function null
+      }
+    }
+}

modules/expo-keyboard-language/expo-module.config.json

@@ -0,0 +1,9 @@
+{
+  "platforms": ["ios", "android"],
+  "ios": {
+    "modules": ["ExpoKeyboardLanguageModule"]
+  },
+  "android": {
+    "modules": ["expo.modules.keyboardlanguage.ExpoKeyboardLanguageModule"]
+  }
+}

modules/expo-keyboard-language/index.ts

@@ -0,0 +1,4 @@
+export {
+  addKeyboardLanguageListener,
+  getCurrentKeyboardLanguage,
+} from './src/index'

modules/expo-keyboard-language/ios/ExpoKeyboardLanguage.podspec

@@ -0,0 +1,20 @@
+Pod::Spec.new do |s|
+  s.name           = 'ExpoKeyboardLanguage'
+  s.version        = '1.0.0'
+  s.summary        = 'Expo module to detect the current keyboard language'
+  s.description    = 'Expo module to detect the current keyboard language'
+  s.author         = ''
+  s.homepage       = 'https://github.com/bluesky-social/social-app'
+  s.platforms      = { :ios => '13.4' }
+  s.source         = { git: '' }
+  s.static_framework = true
+
+  s.dependency 'ExpoModulesCore'
+
+  s.pod_target_xcconfig = {
+    'DEFINES_MODULE' => 'YES',
+    'SWIFT_COMPILATION_MODE' => 'wholemodule'
+  }
+
+  s.source_files = "**/*.{h,m,mm,swift,hpp,cpp}"
+end

modules/expo-keyboard-language/ios/ExpoKeyboardLanguageModule.swift

@@ -0,0 +1,75 @@
+import ExpoModulesCore
+
+public class ExpoKeyboardLanguageModule: Module {
+  public func definition() -> ModuleDefinition {
+    Name("ExpoKeyboardLanguage")
+
+    Events("onKeyboardLanguageChange")
+
+    Function("getCurrentKeyboardLanguage") {
+      return self.currentKeyboardLanguage()
+    }
+
+    OnStartObserving {
+      NotificationCenter.default.addObserver(
+        self,
+        selector: #selector(self.onInputModeOrResponderChange),
+        name: UITextInputMode.currentInputModeDidChangeNotification,
+        object: nil
+      )
+      NotificationCenter.default.addObserver(
+        self,
+        selector: #selector(self.onInputModeOrResponderChange),
+        name: UIResponder.keyboardDidShowNotification,
+        object: nil
+      )
+    }
+
+    OnStopObserving {
+      NotificationCenter.default.removeObserver(
+        self,
+        name: UITextInputMode.currentInputModeDidChangeNotification,
+        object: nil
+      )
+      NotificationCenter.default.removeObserver(
+        self,
+        name: UIResponder.keyboardDidShowNotification,
+        object: nil
+      )
+    }
+  }
+
+  private var lastLanguage: String?
+
+  @objc
+  private func onInputModeOrResponderChange() {
+    let language = currentKeyboardLanguage()
+    if language != lastLanguage {
+      lastLanguage = language
+      sendEvent("onKeyboardLanguageChange", [
+        "language": language as Any
+      ])
+    }
+  }
+
+  private func currentKeyboardLanguage() -> String? {
+    let keyWindow = UIApplication.shared.connectedScenes
+      .compactMap { $0 as? UIWindowScene }
+      .flatMap { $0.windows }
+      .first { $0.isKeyWindow }
+
+    return keyWindow?.findFirstResponder()?.textInputMode?.primaryLanguage
+  }
+}
+
+private extension UIView {
+  func findFirstResponder() -> UIView? {
+    if isFirstResponder { return self }
+    for subview in subviews {
+      if let found = subview.findFirstResponder() {
+        return found
+      }
+    }
+    return nil
+  }
+}

modules/expo-keyboard-language/src/index.native.ts

@@ -0,0 +1,26 @@
+import {type EventSubscription} from 'expo-modules-core'
+import {requireNativeModule} from 'expo-modules-core'
+
+type ExpoKeyboardLanguageModule = {
+  getCurrentKeyboardLanguage(): string | null
+  addListener(
+    eventName: 'onKeyboardLanguageChange',
+    listener: (event: {language: string | null}) => void,
+  ): EventSubscription
+}
+
+const NativeModule = requireNativeModule<ExpoKeyboardLanguageModule>(
+  'ExpoKeyboardLanguage',
+)
+
+export function getCurrentKeyboardLanguage(): string | null {
+  return NativeModule.getCurrentKeyboardLanguage()
+}
+
+export function addKeyboardLanguageListener(
+  cb: (language: string | null) => void,
+): EventSubscription {
+  return NativeModule.addListener('onKeyboardLanguageChange', event => {
+    cb(event.language)
+  })
+}

modules/expo-keyboard-language/src/index.ts

@@ -0,0 +1,11 @@
+import {type EventSubscription} from 'expo-modules-core'
+
+export function getCurrentKeyboardLanguage(): string | null {
+  return null
+}
+
+export function addKeyboardLanguageListener(
+  _cb: (language: string | null) => void,
+): EventSubscription {
+  return {remove() {}}
+}