MKV Cutter forcing subtitles?

[Selur]

As quick solution, you can simply open the file with mkvtoonix-gui, open the header editor and your file and change the 'force display' flag.
Haven't looked at the source code of MKV Cutter for quite some time, but I checked and MKV Cutter, does not set a flag that a subtitle file should be a default or forced track:

// SUBTITLE FILES
  foreach(QString file, subtitleFiles)
  {
    options << "--no-video";
    options << "--no-audio";
    options << "--no-global-tags";
    options << "--no-chapters";
    options << "--no-track-tags";
    options << "--subtitle-tracks";
    options << "0";
    lang = file;
    index = lang.lastIndexOf("_track_");
    if (index != -1) {
      lang = lang.remove(0, index + 7);
      lang = lang.remove(lang.lastIndexOf("."), lang.size()).trimmed();
      index = lang.toInt();
      lang = subtitles.at(index).language;
      if (lang != QString()) {
        options << "--language";
        options << "0:" + lang;
      }
    }
    options << "--compression";
    options << "-1:none";
    options << doubleBackSlash(file);
  }

MKV Cutter doesn't even check whether a stream is flagged as forced or not.
Since I wrote MKV Cutter just as a proof of concept years ago, I don't really have any plan to change it in the near future.
So, the quickest option is to use the mkvtoolnix header editor.

Cu Selur

Ps.: Happy that MKV Cutter is still useful to some users out there.