the special characters are probably not supported by the file system on the drive. There is nothing you can do about this short of renaming the files or possibly changing the file system on the drive. You Mac HDD is most likely formatted in MAC OS extended journaled but the drive is probably in FAT32 or exFAT. Each of these file systems have different characters which cannot be used in a file name. here is a FAQ for best practices for file naming https://support.apple.com/en-us/HT202808
If you do not want to go through the trouble of renaming the files you can try reformatting the drive using disk utility on a Mac. When you format use the file system MAC OS extended journaled. Once this is done it should support the same file names as the HDD on your Mac. The down side of reformatting is cross platform compatibility. If you do this it will only be compatible with Mac computers. If you connect it to a Windows machine or something like a DVD player etc it will not be able to read the format and your files will not be accessible.
