alias subs=subs

function subs() {
    movie="${1}"
    filename="${1%.*}"
    mappings=`ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 "${movie}"`
    OLDIFS=$IFS
    IFS=,
    ( while read idx lang
    do
        echo "Exctracting ${lang} subtitle #${idx} from ${movie}"
        ffmpeg -nostdin -hide_banner -loglevel quiet -i "${movie}" -map 0:"$idx" "${filename}_${lang}_${idx}.srt"
    done <<< "${mappings}" )
    IFS=$OLDIFS
}

function subs() {
    movie="${1}"
    filename="${1%.*}"
    mappings=`ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 "${movie}"`
    OLDIFS=$IFS
    IFS=,
    ( while read idx lang
    do
        echo "Exctracting ${lang} subtitle #${idx} from ${movie}"
        ffmpeg -nostdin -hide_banner -loglevel quiet -i "${movie}" -map 0:"$idx" "${filename}_${lang}_${idx}.srt"
    done <<< "${mappings}" )
    IFS=$OLDIFS
}

subs "$1"

mappings=`ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 "Movie-1080p.mkv"
echo ${mappings}

It should show something like 3,eng.

Then, substitute ${idx} & ${lang} with mapping values, e.g.:

ffmpeg -nostdin -hide_banner -loglevel quiet -i "Movie-1080p.mkv" -map 0:"${idx}" "Movie-1080p_${lang}_${idx}.srt"

#!/usr/bin/env bash

function subs() {
    movie="${1}"
    filename="${1%.*}"
    mappings=`ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 "${movie}"`
    OLDIFS=$IFS
    IFS=,
    ( while read idx lang
    do
        echo "Exctracting ${lang} subtitle #${idx} from ${movie}"
        ffmpeg -nostdin -hide_banner -loglevel quiet -i "${movie}" -map 0:"$idx" "${filename}_${lang}_${idx}.srt"
    done <<< "${mappings}" )
    IFS=$OLDIFS
}

subs "${1}"