Same problem with slave on Jenkins ver. 1.637, thou no problem on master.
file.encoding - UTF-8 file.encoding.pkg - sun.io sun.io.unicode.encoding - UnicodeLittle sun.java.command - /usr/share/jenkins/jenkins.war --webroot=/var/cache/jenkins/war --httpPort=8080 --ajp13Port=-1 java.version - 1.7.0_85 java.vm.name - OpenJDK 64-Bit Server VM java.vm.version - 24.85-b03 sun.java.launcher - SUN_STANDARD sun.jnu.encoding - UTF-8 user.country US user.language en
I fix this problem by adding the following line in ~jenkins/.bashrc on Slave:
export LANG=en_US.UTF-8
Because in the plain text log view the characters are correct, this issue is not related to ssh-slaves-plugin at all.