I use DBI (1.601) and DBD::Oracle all the time and all my data is utf8. I have set NLS_LANG=AMERICAN_AMERICA.AL32UTF8 in my environment and it works fine. I believe NLS_LANG is still in use and still supposed to work - it is a feature picked up by the Oracle client libraries.

Did you set NLS_LANG before connecting? Try setting it your environment and exporting it before running your script. As you don't mention how you came by the latin captital letter a with diaeresis it is difficult to say any more.

IIRC some versions of oracle don't have support for utf8 - some versions or oracle XE I believe.