In SMPlayer 17.12.0, "forced" or "default" attributes on streams in MKV files are ignored. This has been the behavior for many versions, but I kept expecting it to be fixed, so I'm finally posting.
For audio streams, SMPlayer always picks the first audio stream that matches the user language choice. For subtitle streams, no stream in the MKV file is played by default, regardless of the settings on the streams.
I use the "forced" setting on subtitle streams that only contain dialog where there is no audio stream in a spoken language I understand. It's silly to have to manually pick this track, especially when SMPlayer can find matching subtitle tracks that aren't in the MKV file.
I know some users might not like having movies play back the first time respecting the "default" or "forced" flags, so adding an option (that defaults to off) that enables respecting stream settings would be nice.