Yes, there is another error, this the copy of the error :
Warning: array_key_exists() [function.array-key-exists]: The second argument should be either an array or an object in K:\localhost\htdocs\opencart\include\language.php on line 58
I dont know what its mean.
I presume you are using php5, the reason you are getting this error is due to the behavior of array_merge() under PHP 5. Unlike PHP 4, array_merge() now only accepts parameters of type array.
Not to sure if there is a better fix, but I used Type casting to fix the issue, on line 74 of include/language.php change
$this->data = array_merge($this->data, @$_);
$this->data = array_merge((array)$this->data, @$_);
As the name implies, all this is effectively doing is casting $this to an array.
I havent tested this solution extensively, but it should resolve your issue.