IMPDP-ing a dump file that someone has handed me over into Oracle XE results in special characters, i.e. Umlauts, being messed up.
In a hex editor, the dump file shows
a) the token WE8MSWIN1252 near the beginning, but
b) Umlauts obviously being encoded in DOS 850, for example "König" is encoded as 4b 94(!) 6e 69 67.
Does this prove that the dump file is badly formatted and that I have to resign myself to the complicated approach mentioned at the end of <https://forums.oracle.com/message/4142008#4142008>?
Regarding the proof that the import file is corrupted: if you import and you see unexpected characters in Oracle SQL Developer, then this is a pretty good proof. If you see incorrect characters in SQL*Plus, it is not yet a proof, as SQL*Plus itself may be misconfigured.