AppleScript Text Delimiter for most recent text
There are a number of options to enable you to run a regex search in Applescript, which is probably the easiest way to do what you're looking for. The below code is written using Satimage, but you can also use any of the other options with the same regex string.

set regexStr to "(?&lt;={\n)[^{}]*(?=\n}[^}]*\Z)"
find text regexStr in dataBackupFile with regexp and string result


Given the text you provided, this would return:

demo demo demo
demo demo


For completeness sake, I'll just break down the regex:

(?&lt;={\n)[^{}]*(?=\n}[^}]*\Z)
(?&lt;={\n)                     - makes sure the match is immediately preceded by {\n
        [^{}]*               - matches as many non-brackets as it can (your string)
              (?=\n}[^}]*\Z) - makes sure the match is immediately followed by a
                               close bracket, with no more brackets between it and
                               the end of the file


Edit: I just noticed that your example text has been edited by someone else since you first posted. If you actually meant that it's all on one line separated by spaces, you should replace the \ns with spaces.