In several places throughout the org.jgroups.util.Util class, it is assumed that Strings are one byte per character.

For example, see objectToByteBuffer lines 561-567:

https://github.com/belaban/JGroups/blob/master/src/org/jgroups/util/Util.java#L561-L567

case TYPE_STRING:
    String str=(String)obj;
    int len=str.length();
    ByteBuffer retval=ByteBuffer.allocate(Global.BYTE_SIZE + len).put(TYPE_STRING);
    for(int i=0; i < len; i++)
        retval.put((byte)str.charAt(i));
    return retval.array();

This code will incorrectly encode any String with non ASCII encoding.

There are several options to fix. You could use str.getBytes(StandardCharsets.UTF_8) to get a proper byte encoding, or you could use the existing TYPE_SERIALIZABLE code path.