Example mkv adding video, audio, subtitles and languages for each track

Convert subtitles to UTF-8

iconv -f ISO8859_1 -t UTF-8 INFILE.srt > UTF8-OUTFILE.srt

File with French audio track and English subtitles

mkvmerge -o OUTFILE.mkv -A -S video.m4v audio.aac subtitle.srt
mkvmerge -o FINAL.mkv --language 2:fre --language 3:eng OUTFILE.mkv