Yet again a newer version of the MKVToolnix package for Slackware (Sbo build). This one was build on a 14.1 system. Note that this is also the last version that uses the wxWidgets library for the mkvmerge GUI tool (mmg). Newer versions apparently will rely on Qt5. However, Qt5 is not part of a standard Slackware 14.1 system.

 
For Slackware 14.1 x64:

 

Enjoy 🙂