mplayer

subtitles

Normally you would place a file with the same name apart from the extension besides the media file.

movie.mp4
movie.srt

However this does not work with unicode files. Test what the encoding is with the file command.

file Cloud.Atlas.2012.1080p.BrRip.x264.YIFY.dut.srt 
Cloud.Atlas.2012.1080p.BrRip.x264.YIFY.dut.srt: ISO-8859 text, with CRLF line terminators

That one will work fine.

file Ad.Astra.2019.HDRip.XviD.AC3-EVO.srt 
Ad.Astra.2019.HDRip.XviD.AC3-EVO.srt: UTF-8 Unicode (with BOM) text, with CRLF line terminators

That one will show lines like this wrong:

- Oké, we gaan erheen.

Becomes

Ok??, we gaan erheen.

But it is easily circumvented by changing the extension to .utf8

Ad.Astra.2019.HDRip.XviD.AC3-EVO.mp4
Ad.Astra.2019.HDRip.XviD.AC3-EVO.utf8

Or .. just put this in your ~/.mplayer/config file :

utf8=true

The ISO-8859 files will still show ok !!