add android keyboard language change detection

uses ContentObserver on Settings.Secure.SELECTED_INPUT_METHOD_SUBTYPE
to detect when the user switches keyboard language on Android.
deduplicates events like the iOS side.

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

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

@@ -1,31 +1,68 @@
 package expo.modules.keyboardlanguage
 
+import android.database.ContentObserver
 import android.os.Build
+import android.os.Handler
+import android.os.Looper
+import android.provider.Settings
 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() {
+  private var subtypeObserver: ContentObserver? = null
+  private var lastLanguage: String? = null
+
   override fun definition() =
     ModuleDefinition {
       Name("ExpoKeyboardLanguage")
 
-      Function("getCurrentKeyboardLanguage") {
+      Events("onKeyboardLanguageChange")
-        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) {
+      Function("getCurrentKeyboardLanguage") {
-          val tag = subtype.languageTag
+        return@Function getCurrentLanguage()
-          if (tag.isNotEmpty()) return@Function tag
+      }
+
+      OnStartObserving {
+        val context = appContext.reactContext ?: return@OnStartObserving
+        val uri = Settings.Secure.getUriFor("selected_input_method_subtype")
+
+        subtypeObserver = object : ContentObserver(Handler(Looper.getMainLooper())) {
+          override fun onChange(selfChange: Boolean) {
+            val language = getCurrentLanguage()
+            if (language != lastLanguage) {
+              lastLanguage = language
+              sendEvent("onKeyboardLanguageChange", mapOf("language" to language))
+            }
+          }
         }
 
-        @Suppress("DEPRECATION")
+        context.contentResolver.registerContentObserver(uri, false, subtypeObserver!!)
-        val locale = subtype.locale
+      }
-        if (locale.isNotEmpty()) return@Function locale
 
-        return@Function null
+      OnStopObserving {
+        subtypeObserver?.let { observer ->
+          appContext.reactContext?.contentResolver?.unregisterContentObserver(observer)
+        }
+        subtypeObserver = null
       }
     }
+
+  private fun getCurrentLanguage(): String? {
+    val context = appContext.reactContext ?: return null
+    val imm = context.getSystemService<InputMethodManager>() ?: return null
+    val subtype = imm.currentInputMethodSubtype ?: return null
+
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
+      val tag = subtype.languageTag
+      if (tag.isNotEmpty()) return tag
+    }
+
+    @Suppress("DEPRECATION")
+    val locale = subtype.locale
+    if (locale.isNotEmpty()) return locale
+
+    return null
+  }
 }