If you modify the script from this HowTo a bit, you’ll get a way to treat all MKV files in the current folder at once.
So careful where you store it.
The modified command line is C:\Program Files\MKVToolNix\mkvpropedit" --tags all:"" --delete title "%%~nf.mkv"
It will only strip out the movie title tag and additional external metatags from the file. It will leave the language tags and the title and ‘forced’ properties of the streams unchanged.