Bash script to remove accents and special characters from filenames recursively.

strip_bad_filename_characters.sh

#!/usr/bin/env bash
# Recursively remove all special characters from filenames by renaming them to their ASCII normalized forms.
#
# By default it does a dry run, to actually move the files uncomment the `mv -vi ...` line.
#
# This is useful for cleaning up network shares that will be shared via SMB/NFS between Unix/macOS/Windows
# where non-ASCII filenames can sometimes cause "file does not exist" errors when trying to access the files.
#
# This script removes leading/trailing whitespace in filenames and replaces accents and non-english 
# characters with their ASCII equivalent, if no ASCII equivalent exists, it removes the character e.g.:
#    some_name_í.txt -> some_name_i.txt
#    some_name_á.txt -> some_name_a.txt
#    some_name_é.txt -> some_name_e.txt
#    some_name_^.txt -> some_name_.txt
#    some_name_🐞.txt -> some_name_.txt
#    some_name_в.txt -> some_name_.txt

IFS=$'\n'

folder="."
allowed_characters="a-zA-Z0-9_\. \/@#\~&$+()\'!-"
normalize_cmd="
import re
import unicodedata

normalized = unicodedata.normalize('NFD', input()).encode('ascii', 'ignore').decode('utf-8')
stripped = re.sub('[^$allowed_characters]', '', normalized)
print(stripped)"

badfiles=$(
    find "$folder" -name '*'                                           # find all files in the folder recursively
    | grep ".*[^$allowed_characters].*"                                # filter for filenames containing characters allowed the specified charset
    | awk '{ print -length, $0 }' | sort -n -s | cut -d" " -f2-        # sort longest -> shortest so we rename child files before their parent folders to avoid breaking paths
)

for path in $badfiles; do
    oldpath="$path"
    newpath=$(echo "$oldpath" | python3 -c "$normalize_cmd")
    echo "From: $oldpath"
    echo "To:   $newpath"
    # mv -vi -- "$oldpath" "$newpath"
    echo "--------------------------------------------"
done

I adapted this to also transliterate non-Latin characters (in this case Cyrillic/Russian characters) to latin characters. Here is my version if that is interesting for anyone.
(without this, the Cyrillic charcters were just removed as "special" characters, which resulted in many filenames being the same! So, I thought why not keep the info, just in latin chars instead)

#!/usr/bin/env bash
# Recursively remove all special characters from filenames by renaming them to their ASCII normalized forms.
#
# By default it does a dry run, to actually move the files uncomment the `mv -vi ...` line.
#
# This is useful for cleaning up network shares that will be shared via SMB/NFS between Unix/macOS/Windows
# where non-ASCII filenames can sometimes cause "file does not exist" errors when trying to access the files.
#
# This script removes leading/trailing whitespace in filenames and replaces accents and non-english 
# characters with their ASCII equivalent, if no ASCII equivalent exists, it removes the character e.g.:
#    some_name_í.txt -> some_name_i.txt
#    some_name_á.txt -> some_name_a.txt
#    some_name_é.txt -> some_name_e.txt
#    some_name_^.txt -> some_name_.txt
#    some_name_🐞.txt -> some_name_.txt
#    some_name_в.txt -> some_name_v.txt

IFS=$'\n'

folder="."
allowed_characters="a-zA-Z0-9_\. \/()-"
normalize_cmd="
import re
from transliterate import translit
normalized = translit(input(), 'ru', reversed=True)
stripped = re.sub('[^$allowed_characters]', '', normalized)
print(stripped)"

badfiles=$(find "$folder" -name '*' | grep ".*[^$allowed_characters].*" | awk '{ print -length, $0 }' | sort -n -s | cut -d" " -f2-)

for path in $badfiles; do
    oldpath="$path"
    newpath=$(echo "$oldpath" | python3 -c "$normalize_cmd")
    echo "From: $oldpath"
    echo "To:   $newpath"
    mv -vi -- "$oldpath" "$newpath"
    echo "--------------------------------------------"
done

Check detox, replace problematic characters in filenames. More features on apt show detox.