Change class_language.php so the langinfo php file is expected inside the language folder

In light of the internal discussions about managing 1.8's translations I made this change to accommodate for the subtree split of the english language.

This is how languages are structured:

- inc/
    - languages/
        - english/
            - ...
        - **english.php**

After this change languages would be structured like so:

- inc/
    - languages/
        - english/
            - ...
            - **english.php**