GLib.filename_to_utf8

function filename_to_utf8(opsysstring: String, len: Number(gssize), bytes_read: Number(gsize), bytes_written: Number(gsize)): String {
    // Gjs wrapper for g_filename_to_utf8()
}

Converts a string which is in the encoding used by GLib for filenames into a UTF-8 string. Note that on Windows GLib uses UTF-8 for filenames; on other platforms, this function indirectly depends on the [current locale][setlocale].

opsysstring: a string in the encoding for filenames
len: the length of the string, or -1 if the string is nul-terminated (Note that some encodings may allow nul bytes to occur inside strings. In that case, using -1 for the len parameter is unsafe)
bytes_read: location to store the number of bytes in the input string that were successfully converted, or null. Even if the conversion was successful, this may be less than len if there were partial characters at the end of the input. If the error #G_CONVERT_ERROR_ILLEGAL_SEQUENCE occurs, the value stored will the byte offset after the last valid input sequence.
bytes_written: the number of bytes stored in the output buffer (not including the terminating nul).
Returns: The converted string, or null on an error.