I am running Windows 7. With a Pure installation of Geoserver 2.12.1 (2.12.0 is the same).
First image is showing that geoserver after 2.12 version has troubles with cyrrilic layer's names. Second is showing that if version is under 2.12, problem is gone.
Same data_dir, layers files and pure installations with default settings.
-Dfile.encoding=UTF8 config is useless.