activateVideoTrack(srclang) {
    // parse through TextTrackList (not an Array)
    for (let i = 0; i < this.node.textTracks.length; i++) {
      const track = this.node.textTracks[i];
      // For the 'subtitles-off' button, the first condition will never match so all will subtitles be turned off
      if (track.kind === 'subtitles' || track.kind === 'captions') {
        if (track.language === srclang) {
          track.mode = 'showing';
          if (this.options.toggleCaptionsButtonWhenOnlyOne && this.getSubtitles().length === 1) {
            // activate captions toggle button
            this.captionsButton.classList.add(`${this.options.classPrefix}captions-button-toggle-on`);
          }
        } else {
          track.mode = 'hidden';
        }
      }
    }
  }
Display a specific language and hide all other subtitles/captions.
@param {string} srclang Language code of the subtitles to display