Stop Token Filter Language Customization Not Working in Java

Hi everyone, I'm trying to create a customized Indonesian language stop token filter using the Java package.
The following json is how the configuration looks like when using curl (which works just fine):

"filter": { 
    "my_stop_filter": { 
        "type": "stop", 
        "stopwords": "_indonesian_"
    }
}

And then, here's how I tried to recreate it using Java:

private TokenFilter createStopFilter() { 
    return new TokenFilter.Builder() 
        .definition( 
            new TokenFilterDefinition.Builder() 
                .stop(new StopTokenFilter.Builder().stopwords("_indonesian_").build()) 
                .build() 
            ) 
           .build(); 
}

Turns out, the stopwords just filter the word "_ indonesian _" instead of the built-in Indonesian stop words like it was supposed to do.
The documentation for the Java package also doesn't mention any support for language customization.
Does this mean it's simply not supported in Java? Or did I do something wrong?
Thanks in advance!