mahendra, what theme do you have now?
Please test if the problem persists on the default theme. Switch to default theme and try to check it once again and if the problem still persists - provide us with the step-by-step instructions on how to reproduce the problem.
mahendra, we can not reproduce this issue on our Demo. Please check the language key value. Go to the Admin Area>Settings>Language section and find the 'mailbox+write_reply' language key and the value should be "Write a reply...".