code: public ApnsPayloadBuilder setLocalizedAlertSubtitle(final String localizedAlertSubtitleKey, final String... alertSubtitleArguments) {
          this.localizedAlertSubtitleKey = localizedAlertSubtitleKey;
          this.localizedAlertSubtitleArguments = (alertSubtitleArguments != null && alertSubtitleArguments.length > 0) ? alertSubtitleArguments : null;
  
          this.alertSubtitle = null;
  
          return this;
      }
docs: <p>Sets the key of the subtitle string in the receiving app's localized string list to be shown for the push
  notification. Clears any previously-set literal subtitle. The message in the app's string list may optionally
  have placeholders, which will be populated by values from the given {@code alertSubtitleArguments}.</p>
  
  <p>By default, no subtitle is included. Requires iOS 10 or newer.</p>
  
  @param localizedAlertSubtitleKey a key to a string in the receiving app's localized string list
  @param alertSubtitleArguments arguments to populate placeholders in the localized subtitle string; may be
  {@code null}
  
  @return a reference to this payload builder
  
  @since 0.8.1