Re-apply the locale override to the configuration if necessary

app/k9mail/src/main/java/com/fsck/k9/App.kt

@@ -2,6 +2,7 @@ package com.fsck.k9
 
 import android.app.Application
 import android.content.res.Configuration
+import android.content.res.Resources
 import com.fsck.k9.activity.MessageCompose
 import com.fsck.k9.controller.MessagingController
 import com.fsck.k9.external.MessageProvider
@@ -25,6 +26,7 @@ class App : Application() {
     private val themeManager: ThemeManager by inject()
     private val appLanguageManager: AppLanguageManager by inject()
     private val appCoroutineScope: CoroutineScope = GlobalScope + Dispatchers.Main
+    private var appLanguageManagerInitialized = false
 
     override fun onCreate() {
         Core.earlyInit(this)
@@ -46,13 +48,14 @@ class App : Application() {
 
     private fun initializeAppLanguage() {
         appLanguageManager.init()
-        applyOverrideLocale()
+        applyOverrideLocaleToConfiguration()
+        appLanguageManagerInitialized = true
         listenForAppLanguageChanges()
     }
 
-    private fun applyOverrideLocale() {
+    private fun applyOverrideLocaleToConfiguration() {
         appLanguageManager.getOverrideLocale()?.let { overrideLocale ->
-            updateConfigurationWithLocale(resources.configuration, overrideLocale)
+            updateConfigurationWithLocale(superResources.configuration, overrideLocale)
         }
     }
 
@@ -61,14 +64,14 @@ class App : Application() {
             .drop(1) // We already applied the initial value
             .onEach { overrideLocale ->
                 val locale = overrideLocale ?: Locale.getDefault()
-                updateConfigurationWithLocale(resources.configuration, locale)
+                updateConfigurationWithLocale(superResources.configuration, locale)
             }
             .launchIn(appCoroutineScope)
     }
 
     override fun onConfigurationChanged(newConfiguration: Configuration) {
-        applyOverrideLocale()
-        super.onConfigurationChanged(resources.configuration)
+        applyOverrideLocaleToConfiguration()
+        super.onConfigurationChanged(superResources.configuration)
     }
 
     private fun updateConfigurationWithLocale(configuration: Configuration, locale: Locale) {
@@ -79,7 +82,31 @@ class App : Application() {
         }
 
         @Suppress("DEPRECATION")
-        resources.updateConfiguration(newConfiguration, resources.displayMetrics)
+        superResources.updateConfiguration(newConfiguration, superResources.displayMetrics)
+    }
+
+    private val superResources: Resources
+        get() = super.getResources()
+
+    // Creating a WebView instance triggers something that will cause the configuration of the Application's Resources
+    // instance to be reset to the default, i.e. not containing our locale override. Unfortunately, we're not notified
+    // about this event. So we're checking each time someone asks for the Resources instance whether we need to change
+    // the configuration again. Luckily, right now (Android 11), the platform is calling this method right after
+    // resetting the configuration.
+    override fun getResources(): Resources {
+        val resources = super.getResources()
+
+        if (appLanguageManagerInitialized) {
+            appLanguageManager.getOverrideLocale()?.let { overrideLocale ->
+                if (resources.configuration.currentLocale != overrideLocale) {
+                    Timber.w("Resources configuration was reset. Re-applying locale override.")
+                    appLanguageManager.applyOverrideLocale()
+                    applyOverrideLocaleToConfiguration()
+                }
+            }
+        }
+
+        return resources
     }
 
     companion object {

app/ui/base/src/main/java/com/fsck/k9/ui/base/AppLanguageManager.kt

@@ -45,6 +45,12 @@ class AppLanguageManager(
         setLocale(appLanguage)
     }
 
+    fun applyOverrideLocale() {
+        currentOverrideLocale?.let { overrideLocale ->
+            Locale.setDefault(overrideLocale)
+        }
+    }
+
     private fun setLocale(appLanguage: String) {
         val overrideLocale = getOverrideLocaleForLanguage(appLanguage)
         currentOverrideLocale = overrideLocale