UTF8 should not be required for eZ Find and eZP3. If you have a test environment available, please try to comment out these two lines in <i>extension/ezfind/java/solr/conf/schema.xml</i>
It looks you found the problem. The resolution for this is to use eZ Find to convert the data to UTF-8 before it's indexed. Please add a bug report about this in the issue tracker, and I'll fix it as soon as I have time.