On English Windows environment, jcmd prints "Invalid agent state" as RuntimeException message if ManagementAgent.start is executed twice.
But the message is corrupted on Japanese Windows environment.

English Windows environment:

jcmd Test ManagementAgent.start jmxremote.port=50082 jmxremote.authenticate=false jmxremote.ssl=false
16942:
java.lang.RuntimeException: Invalid agent state: Agent already started

Japanese Windows environment:

jcmd Test ManagementAgent.start jmxremote.port=50082 jmxremote.authenticate=false jmxremote.ssl=false
7368:
java.lang.RuntimeException: 繧ｨ繝ｼ繧ｸ繧ｧ繝ｳ繝医?ｮ迥ｶ諷九′辟｡蜉ｹ縺ｧ縺?: Agent already started

The java process throws RuntimeException at jdk.management.agent/jdk.internal.agent.Agent.startRemoteManagementAgent(Agent.java:340).

    throw new RuntimeException(getText(INVALID_STATE, "Agent already started"));

The japanese exception message is defined in ./jdk.management.agent/share/classes/jdk/internal/agent/resources/agent_ja.properties
with utf8 charset, and it is built in jdk/internal/agent/resources/agent_ja.class.

    agent.err.invalid.state = \u30A8\u30FC\u30B8\u30A7\u30F3\u30C8\u306E\u72B6\u614B\u304C\u7121\u52B9\u3067\u3059: {0}

On the other hand,
the jcmd reads the message at jdk.attach/sun.tools.attach.HotSpotVirtualMachine.readErrorMessage(HotSpotVirtualMachine.java:360).

        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        while ((s = br.readLine()) != null) {

The message is read without specifying a charset and the default charset is not utf8.

This is the reason why the exception message of jcmd ManagementAgent.start is corrupted in Japanese Windows.

This does not occur since jdk18 owing to JEP 400: UTF-8 by Default.