Issues with diacritics in filename… | Apple Developer Forums

Issues with diacritics in filename on iOS when the system main language is not English

Hi, I'm encountering a weird issue on iOS that happens:

for files with diacritics in their name, like "Gòmez.pdf" or "Télé.mp4",
when the iPhone or iPad main language is not set to English,
if the file has been created with a relatively low-level Unix function like fopen() or copyfile().

Then, the file cannot be previsualized using QuickLook or opened using other apps. Most of the time it fails silently, but on some occasions I get the following error message: "You do not have permission to save the file "filename.pdf" in the folder "myFolder"".

The issue is present in, at least, iOS 16 and 26. It seems worse in iOS 26. It seems that all three conditions are required, I don't see the issue when the iPhone or iPad is set to use English as the main language. I also don't see the issue if I rename the files in the Files app.

I'm probably doing something wrong, but what can it be?

(it's kind of weird that my recommendation for users becomes: if you want to use international characters in your file names, you need to set the iPad language to English...)