Logstasch eventlog event fieds is written to kafka in chinese

[gititc]

I'm trying to write event log messages from specific source to kafka.
The problem is that all textual event fields are written to kafka in chinese.
Because of that:

1. filter is not working (the if statement for specific source is wrong because source nume equals to chinese instead of real value)
2. when removing the filter all textual event fileds are shown in chinese in kafka.
   (writing just text works fine)
   tried also to add encoding without success.

here is my configuration:
input {
eventlog {
logfile => 'Application'
codec => plain{
charset => 'Windows-31J'
}
}
}

output {
kafka {
codec => "json"
bootstrap_servers => "10.1.70.101:9092"
topic_id => "eventlog"
}
}

and here is my output in kafka:

{"EventType":"湩潦浲瑡潩�","TimeGenerated":"2018-02-07T09:54:03.000Z","@version":"1","SourceName":"畏汴潯�","host":"m2044248-w7","Category":0,"ComputerName":"㉭㐰㈴㠴眭⸷汴⹶潧⹶汩","User":null,"EventIdentifier":63,"Logfile":"Application","@timestamp":"2018-02-07T11:04:33.524Z","RecordNumber":177273,"InsertionStrings":["桔⁥硅档湡敧眠扥猠牥楶散爠煥敵瑳䜠瑥灁䵰湡晩獥獴猠捵散摥摥‮"],"TimeWritten":"2018-02-07T09:54:03.000Z","Type":"湩潦浲瑡潩�","message":"桔⁥硅档湡敧眠扥猠牥楶散爠煥敵瑳䜠瑥灁䵰湡晩獥獴猠捵散摥摥�"}

I'll be very gratefull for your help !
thanks,
Gitit