Fix capitalization of language in track selector

Issue: #9452
PiperOrigin-RevId: 400680794

RELEASENOTES.md

@@ -35,6 +35,8 @@
         `Player.addListener`.
     *   Fix initial timestamp display in `PlayerControlView`
         ([#9524](https://github.com/google/ExoPlayer/issues/9254)).
+    *   Fix capitalization of languages in the track selector
+        ([#9452](https://github.com/google/ExoPlayer/issues/9452)).
 *   Extractors:
     *   MP4: Correctly handle HEVC tracks with pixel aspect ratios other than 1.
     *   TS: Correctly handle HEVC tracks with pixel aspect ratios other than 1.

library/common/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -2243,6 +2243,11 @@ public final class Util {
     return systemLocales;
   }
 
+  /** Returns the default {@link Locale.Category#DISPLAY DISPLAY} {@link Locale}. */
+  public static Locale getDefaultDisplayLocale() {
+    return Util.SDK_INT >= 24 ? Locale.getDefault(Locale.Category.DISPLAY) : Locale.getDefault();
+  }
+
   /**
    * Uncompresses the data in {@code input}.
    *

library/ui/src/main/java/com/google/android/exoplayer2/ui/DefaultTrackNameProvider.java

@@ -104,8 +104,14 @@ public class DefaultTrackNameProvider implements TrackNameProvider {
     if (TextUtils.isEmpty(language) || C.LANGUAGE_UNDETERMINED.equals(language)) {
       return "";
     }
-    Locale locale = Util.SDK_INT >= 21 ? Locale.forLanguageTag(language) : new Locale(language);
-    return locale.getDisplayName();
+    Locale languageLocale =
+        Util.SDK_INT >= 21 ? Locale.forLanguageTag(language) : new Locale(language);
+    Locale displayLocale = Util.getDefaultDisplayLocale();
+    String languageName = languageLocale.getDisplayName(displayLocale);
+    // Capitalize the first letter. See: https://github.com/google/ExoPlayer/issues/9452.
+    int firstCodePointLength = languageName.offsetByCodePoints(0, 1);
+    return languageName.substring(0, firstCodePointLength).toUpperCase(displayLocale)
+        + languageName.substring(firstCodePointLength);
   }
 
   private String buildRoleString(Format format) {