thanks for your prompt reply.
I tried in 2 ways.
1. I downloaded English lang file to my machine by means of core ftp. I modified on note pad and saved with utf8 and uploaded. ( that is the way what i normally do file modifications several times before). The result was unable to upload. repeatedly asking to upload again and again
2. so i went to control pane of serverl. I opened files and tried to edit on built in editor. error message again, saying time out.
I also change particular folder and file permission to writeable. no luck
In fact, in my knowledge, similar thing happened before when I tried to edit web based RSS feeder integrated on my website.
thanks