One of the steps when importing attachments from a data export is to rename the actual attachment files back to their real name because the real name is replaced with a record id in the data export.
If the filenames contain international characters, such as umlauts, these can be replaced with 'garbage' characters when you perform the rename operation at the Windows command line.
To stop this happening, type 'chcp 1252' at theWindows command linebefore performing the rename. This changes the Code Page
so that the characters are recognised and retained in the renamed filename.
For more information, see:
How do I import attachments using my Data Export files?
Renaming exported Attachments/Documents files in a data export
CHCP