Ok thank you.
I downloaded from github the teste case.
If I run the test with an UTF-8 eclipse workspace, runs fine too.
But, running from an ISO-8859-1 eclipse workspace the problem occurs.
See, we are developping the applications inside an ISO-8859-1 workspace. Before the 5.12.1 release, everithing was running fine.
To keep the application running I had to extend the StandaloneProcessEngineConfiguration and set a different BpmnParseFactory (there is no easy way to do this). At the end, I had to change from UTF-8 to ISO-8859-1.
In the test case I had tryied to replace the BpmnXMLConverter to my ISO88591BpmnXMLConverter, but does not work. Because the static method writeRootElement of the DefinitionsRootExport class has defined UTF-8 encoding hardcoded.