Attached please find two build logs, one from maven version 3.3.9, and another from maven version 3.5.2. Both log files were made for the same Java project on Windows 10 machine, with "mvn compile > log" command. Java platform default encoding is UTF-8.
One Java source file contains intentional error, which is reported in lines 433-435 of file "maven.3.3.9.log", and in lines 437-439 of file "maven.3.5.2.log".
Class name is non-ascii and version 3.3.9 log appears right. But in version 3.5.2 this same filename appears unreadable in the error message in the maven log.
Notice that if I view the file "maven.3.5.2.log" with different encoding (cp866), then this error message becomes readable. It looks like this non-ascii filename gets inserted into UTF-8 encoded log file in wrong "cp866" encoding, in maven version 3.5.2.
Still, version 3.3.9 of maven does the right thing, and the error message is readable in UTF-8 log.