Thanks for your reply.
Logstash didn't do anything cause the encoded file was considered as a single line, so i added CR end of line and now it displays characters like these "����@@@@"
i tried almost all the charset values available here https://www.elastic.co/guide/en/logstash/current/plugins-codecs-plain.html
It doesn't seem to work.
With talend i can decode the file with IBM500 charset but it's not available in plain codec.
Any help please to do it with logstash ?