webkitRelativePath in input tag, file type

Hello everyone
I have a problem when I use the ‘input’ tag of ‘file’ type

<input id = "selectLocaldata" ... onChange = "inputDataChange()"
multiple webkitdirectory type = "file" />

inputDataChange = function () {
    let fl = document.getElementById ('selectLocaldata'). files;
    for (let f of fl) {
        str = f.webkitRelativePath;

In ‘webkitRelativePath’, accented characters are double-byte and hence 2 characters.
for example “è” is “e” + charCode(768)
How to bring back this ‘webkitRelativePath’ string in ‘normal’ encoding. (UTF8 I think).

Your solutions will be welcome