Encapsulate Formatters in PlayerHelper

and reset them when the language is changed/changing.
This way they will be re-initialized on the next call.

Also Remove a bunch of outdated/non-thread safe code (STRING_FORMATTER)

app/src/main/java/org/schabi/newpipe/player/helper/PlayerHelper.java

@@ -33,11 +33,9 @@ import com.google.android.exoplayer2.trackselection.ExoTrackSelection;
 import com.google.android.exoplayer2.ui.AspectRatioFrameLayout;
 import com.google.android.exoplayer2.ui.AspectRatioFrameLayout.ResizeMode;
 import com.google.android.exoplayer2.ui.CaptionStyleCompat;
-import com.google.android.exoplayer2.util.MimeTypes;
 
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.extractor.InfoItem;
-import org.schabi.newpipe.extractor.MediaFormat;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
 import org.schabi.newpipe.extractor.stream.SubtitlesStream;
@@ -47,13 +45,14 @@ import org.schabi.newpipe.player.playqueue.PlayQueue;
 import org.schabi.newpipe.player.playqueue.PlayQueueItem;
 import org.schabi.newpipe.player.playqueue.SinglePlayQueue;
 import org.schabi.newpipe.util.ListHelper;
+import org.schabi.newpipe.util.Localization;
 
 import java.lang.annotation.Retention;
 import java.text.DecimalFormat;
+import java.text.DecimalFormatSymbols;
 import java.text.NumberFormat;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.Formatter;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
@@ -62,11 +61,7 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
 public final class PlayerHelper {
-    private static final StringBuilder STRING_BUILDER = new StringBuilder();
+    private static final FormattersProvider FORMATTERS_PROVIDER = new FormattersProvider();
-    private static final Formatter STRING_FORMATTER =
-            new Formatter(STRING_BUILDER, Locale.getDefault());
-    private static final NumberFormat SPEED_FORMATTER = new DecimalFormat("0.##x");
-    private static final NumberFormat PITCH_FORMATTER = new DecimalFormat("##%");
 
     @Retention(SOURCE)
     @IntDef({AUTOPLAY_TYPE_ALWAYS, AUTOPLAY_TYPE_WIFI,
@@ -91,6 +86,10 @@ public final class PlayerHelper {
 
     // region Exposed helpers
 
+    public static void resetFormat() {
+        FORMATTERS_PROVIDER.reset();
+    }
+
     @NonNull
     public static String getTimeString(final int milliSeconds) {
         final int seconds = (milliSeconds % 60000) / 1000;
@@ -98,23 +97,24 @@ public final class PlayerHelper {
         final int hours = (milliSeconds % 86400000) / 3600000;
         final int days = (milliSeconds % (86400000 * 7)) / 86400000;
 
-        STRING_BUILDER.setLength(0);
+        final Formatters formatters = FORMATTERS_PROVIDER.formatters();
-        return (days > 0
+        if (days > 0) {
-                ? STRING_FORMATTER.format("%d:%02d:%02d:%02d", days, hours, minutes, seconds)
+            return formatters.stringFormat("%d:%02d:%02d:%02d", days, hours, minutes, seconds);
-                : hours > 0
+        }
-                ? STRING_FORMATTER.format("%d:%02d:%02d", hours, minutes, seconds)
+
-                : STRING_FORMATTER.format("%02d:%02d", minutes, seconds)
+        return hours > 0
-        ).toString();
+            ? formatters.stringFormat("%d:%02d:%02d", hours, minutes, seconds)
+            : formatters.stringFormat("%02d:%02d", minutes, seconds);
     }
 
     @NonNull
     public static String formatSpeed(final double speed) {
-        return SPEED_FORMATTER.format(speed);
+        return FORMATTERS_PROVIDER.formatters().speed().format(speed);
     }
 
     @NonNull
     public static String formatPitch(final double pitch) {
-        return PITCH_FORMATTER.format(pitch);
+        return FORMATTERS_PROVIDER.formatters().pitch().format(pitch);
     }
 
     @NonNull
@@ -487,5 +487,42 @@ public final class PlayerHelper {
                 player.getContext().getString(R.string.seek_duration_default_value))));
     }
 
+    // endregion
+    // region Format
+
+    static class FormattersProvider {
+        private Formatters formatters;
+
+        public Formatters formatters() {
+            if (formatters == null) {
+                formatters = Formatters.create();
+            }
+            return formatters;
+        }
+
+        public void reset() {
+            formatters = null;
+        }
+    }
+
+    record Formatters(
+        Locale locale,
+        NumberFormat speed,
+        NumberFormat pitch) {
+
+        static Formatters create() {
+            final Locale locale = Localization.getAppLocale();
+            final DecimalFormatSymbols dfs = DecimalFormatSymbols.getInstance(locale);
+            return new Formatters(
+                locale,
+                new DecimalFormat("0.##x", dfs),
+                new DecimalFormat("##%", dfs));
+        }
+
+        String stringFormat(final String format, final Object... args) {
+            return String.format(locale, format, args);
+        }
+    }
+
     // endregion
 }

app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java

@@ -16,6 +16,7 @@ import androidx.preference.Preference;
 import org.schabi.newpipe.DownloaderImpl;
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.extractor.NewPipe;
+import org.schabi.newpipe.player.helper.PlayerHelper;
 import org.schabi.newpipe.util.Localization;
 import org.schabi.newpipe.util.image.ImageStrategy;
 import org.schabi.newpipe.util.image.PicassoHelper;
@@ -53,6 +54,7 @@ public class ContentSettingsFragment extends BasePreferenceFragment {
                 final Intent intent = new Intent(Settings.ACTION_APP_LOCALE_SETTINGS)
                         .setData(Uri.fromParts("package", requireContext().getPackageName(), null));
                 startActivity(intent);
+                PlayerHelper.resetFormat();
                 return true;
             });
             newAppLanguagePref.setVisible(true);
@@ -64,6 +66,7 @@ public class ContentSettingsFragment extends BasePreferenceFragment {
             final String systemLang = getString(R.string.default_localization_key);
             final String tag = systemLang.equals(language) ? null : language;
             AppCompatDelegate.setApplicationLocales(LocaleListCompat.forLanguageTags(tag));
+            PlayerHelper.resetFormat();
             return true;
         });
     }