this script will change the encoding from whatever to UTF-8

subfixer.sh

#!/bin/bash
#you may need to install uchardet package first. sudo apt install uchardet
# https://github.com/BYVoid/uchardet

#replace underscore with white-space !important (iconv cannot find files with white-space in their name)
find -name "* *.srt" -type f | rename 's/ /_/g'

for sub in *.srt;
do
  encode="$(uchardet "${sub}")"
  if [ "$encode" == "x-mac-cyrillic" ]
    then encode="WINDOWS-1256"
  fi
  iconv -f "${encode}" -t UTF-8 "${sub}" -o "${sub}.tmp" && mv -f "${sub}.tmp" "${sub}" && echo "${sub} - *fixed*"
done
echo "done."