First of all, there is an issue in the Core.
#3169212: Improve transliteration of Ukrainian letters →
Adding Ukrainian transliteration data for the PhpTransliteration class fixes the Core issue.
But after that this module still ignores rules for Ukrainian letters transliterating filenames.
Upload any file with name containing letters "И", "и", "Ї", "ї", "Є", "є".
"И", "и" are transliterated to "i", but must be "y".
"Ї", "ї" are transliterated to "i", but must be "yi".
"Є", "є" are transliterated to "e", but must be "ye".
1. Add Ukrainian transliteration data for the PhpTransliteration class to Core.
(Currently: Apply patch from comment #4 on
#3169212-4: Improve transliteration of Ukrainian letters →
).
2. Use it by this module to transliterate filenames.
Closed: won't fix
1.0
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Closing this issue as "wont fix". This contrib module is now obsolete and superseded by the new "opt-in" filename sanitization functionality added to Drupal core in version 10.2. I don't believe the approach in Drupal core suffers from this issue as mentioned in the previous comment.
See Change Record #2972665: New filename sanitization settings during upload (via UI or REST), new sanitization Event, changes to FileUploadResource constructor → for more information.