Í am currently testing the software and it looks good.
I've only got an issue with dutch subtitles.

Setting the default to nl or nld in settings, does not achieve anything.
Workaround is to select the subtitle on each individual file.
This works, but causes the picture to be stretched. No issue with the workaround already posted here by eithet setting the device on 4:3 or use a different profile.

However when using a Video_TS folder as the source, one has to select the subtitle on each individual file.
Even worse on using the "Watch folder" having to select the subtitle on each individual cell.

What am I doing wrong here ?

You can use a playback through a folder Transcoding or turn on "Creating DVD-structure folders for DVD-directories" (Settings - "Media-Resources" - Scanning).

Thx, the "creating dvd structure..." works.
Only thing is that it shows one large file for the complete movie and multiple small files(cells) for the chapter.
One large file is good, but I am not able to skip through the chapters(cells)
To do that I would neet to set subtitling on each individual cell.

A good option would be to be able to set the subtitle in the transcoding profile as you can set the profile at once over multiple files. Maybe it can already be done, but I haven't found out how yet.

A script to set a subtitle language

Settings - Processing - Add
Name: Select Subtitle
Click "Button on the main form"
Script:

procedure ProcessItem(const aItem: TWmsScriptMediaItem; const aLanguage: string);
var
  i, j: Integer;  
  sSubtitleList: string;
begin
  if VarToStr(aItem.Properties[mpiVideoCodec]) <> '' then begin
    sSubtitleList := VarToStr(aItem.Properties[mpiSubtitleList]);
    if sSubtitleList <> '' then begin
      i := Pos(aLanguage, sSubtitleList);
      if i > 0 then begin      
        j := i + Length(aLanguage);
        while (j <= Length(sSubtitleList)) and (sSubtitleList[j] <> ',') do
          Inc(j);          
        aItem.Properties[mpiSubtitleLanguage] := Copy(sSubtitleList, i, j - i)
      end
    end            
  end else if aItem.HasChildItems then   
    for i := 0 to aItem.ChildCount - 1 do    
      ProcessItem(aItem.ChildItems[i], aLanguage)
end;

begin
  if WmsCurrentMediaTreeItem <> nil then begin
    WmsShowInformation('Set subtitle language...');
    try      
      ProcessItem(WmsCurrentMediaTreeItem, 'nl');
    finally
      WmsHideInformation
    end      
  end;                         
  WmsDatabaseAutoSave;  
  ShowMessage('Setting the subtitle language completed');
  ProcessMediaResult := True
end.

Usage:
1. Select folder in Folders [Movies]
2. Click "Select Subtitle"

Great, thx very much. This works.