Checking button text with applescript
You can check every button of the window and wait until one is titled like you want :


property btnTitle : "Run Cleaner"

set btnFound to false

tell application "/Applications/CCleaner.app" to activate

tell application "System Events"
    tell application process "CCleaner"
        click button btnTitle of window 1
        delay 1

        -- Start checking every seconds if window 1 contains a button titled "Run Cleaner"      
        repeat while not btnFound
            repeat with btn in buttons of window 1
                try -- Some buttons don't have title which would return an error if not in try
                    if (title of btn is btnTitle) then
                        set btnFound to true
                    end if
                end try
            end repeat
            delay 1
        end repeat

    end tell
end tell

if btnFound then
    -- Do more stuff
end if