Gets translation data.
The structure is similar to the form API in the way that it is a possibly nested array with the following properties whose presence indicate that the current element is a text that might need to be translated.
The key can be an alphanumeric string.
array $key: If present, only the subarray identified by key is returned.
string $index: Optional index of an attribute below $key.
array A structured data array.
public function getData($key = array(), $index = NULL);