

* MKVToolNix GUI: multiplexer, header editor: added menu entries & keyboard shortcuts for setting the language of the currently selected tracks to one from a configurable list of languages. `Ctrl+Alt+F, D` (that's `Ctrl` and `Alt` with `F` simultaneously followed by `D` without any other key pressed) for toggling the "default track" flag. * MKVToolNix GUI: multiplexer, header editor: added several menu entries & keyboard shortcuts for toggling various track flags of the currently selected tracks, e.g. * MKVToolNix GUI: multiplexer: added support for the "track enabled" track header flag. * mkvmerge: MP4 reader: `mkvmerge` will now evaluate the `flags` field of the track header atom (`tkhd`) and set the track's "enabled" flag accordingly. * mkvmerge: added a new option `-track-enabled-flag` to set or unset the "track enabled" track header flag.

Existing third-party programs will continue working as they are. What will remain unchanged is the property names for those flags in mkvmerge's identification output.

However, the old names will be supported and recognized indefinitely. * mkvmerge: the options `-default-track` and `-forced-track` have been renamed to `-default-track-flag` and `-forced-display-flag` respectively for improved consistency with other option names & the wording used in the GUI.
