diff --git a/RELEASENOTES.md b/RELEASENOTES.md
index 9c0f2962fc..ae01c34f4c 100644
--- a/RELEASENOTES.md
+++ b/RELEASENOTES.md
@@ -88,6 +88,8 @@
     *   Notify onBufferingEnded when the state of origin player becomes
         STATE_IDLE or STATE_ENDED.
     *   Allow to remove all playlist items that makes the player reset.
+*   IMA extension:
+    *   Set the overlay language based on the device locale by default.
 
 ### 2.12.1 (2020-10-23) ###
 
diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
index 27e708a67d..8bb6057a56 100644
--- a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
@@ -58,6 +58,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 
 /**
@@ -544,7 +545,9 @@ public final class ImaAdsLoader implements Player.EventListener, AdsLoader {
   private static final class DefaultImaFactory implements ImaUtil.ImaFactory {
     @Override
     public ImaSdkSettings createImaSdkSettings() {
-      return ImaSdkFactory.getInstance().createImaSdkSettings();
+      ImaSdkSettings settings = ImaSdkFactory.getInstance().createImaSdkSettings();
+      settings.setLanguage(getImaLanguageCodeForDefaultLocale());
+      return settings;
     }
 
     @Override
@@ -585,5 +588,16 @@ public final class ImaAdsLoader implements Player.EventListener, AdsLoader {
       return ImaSdkFactory.getInstance()
           .createAdsLoader(context, imaSdkSettings, adDisplayContainer);
     }
+
+    /**
+     * Returns a language code that's suitable for passing to {@link ImaSdkSettings#setLanguage} and
+     * corresponds to the device's {@link Locale#getDefault() default Locale}.
+     */
+    // TODO: It may be possible to define a better mapping onto IMA's supported language codes. See:
+    // https://developers.google.com/interactive-media-ads/docs/sdks/android/client-side/localization.
+    // IMA will fall back to its default language code ("en") if the value returned is unsupported.
+    private static String getImaLanguageCodeForDefaultLocale() {
+      return Util.splitAtFirst(Util.getSystemLanguageCodes()[0], "-")[0];
+    }
   }
 }