I am new in Joomla. I have recently update my version from joomla 2.5 to joomla 3.8.11.
I had replace all files of jomlaa 3.8.11 to root directories.
When I access admin side, It gives me error : 
Notice: Constant QQ already defined in C:\xampp\htdocs[main_folder]\libraries\src\Language\Language.php on line 18
Anyone master here who can fix it ?