Sorry for late reply to this,
It seems like Jomsocial changed something from the code, can you provide us with your Joomla backend and FTP access so we can help you check on this? Also, may i know which title you want to change to?
I have checked this file in your site and it seems to be working correctly when I changed the string. Here is my screenshot: http://screencast.com/t/wyQv1YlQR3 . Am I missing anything here?
Oh, I am sorry for the confusion. Have you clear your browser and your site cache? Because I have successfully change this language string on Peter's site. If this issue is still persist, perhaps you can create a new ticket on this issue and do provide us with backend access and FTP access so that we can assist you further on this issue.