Change mkv container to mp4 - with subtitles and all audio channels
ffmpeg -i test.mkv -c copy -map 0:4 -map 0:3 -map 0:2 -map 0:1 -map 0:0 -c:s mov_text test.mp4
Batch:
for i in *.mkv; do ffmpeg -i "$i" -c copy -map 0:1 -map 0:0 -c:s mov_text "${i%.*}.mp4"; done