A diferença é o character set usado pelo banco.
Oracle Database 10g Express Edition (Western European)
Single-byte LATIN1 database for Western European language storage, with the Database Homepage user interface in English only.
Oracle Database 10g Express Edition (Universal)
Multi-byte Unicode database for all language deployment, with the Database Homepage user interface available in the following languages: Brazilian Portuguese, Chinese (Simplified and Traditional), English, French, German, Italian, Japanese, Korean and Spanish.