L and LA_ replacement code in Twig ignores LA_ assigned variables

Both the L and LA_ variables used in Twig ( https://github.com/phpbb/phpbb/blob/3.1.x/phpBB/phpbb/template/twig/lexer.php#L113-L117 ) are calling the lang ( https://github.com/phpbb/phpbb/blob/3.1.x/phpBB/phpbb/template/twig/extension.php#L167-L184 ) method in our twig extension. However, the lang function only checks if a L_ variant is assigned_var'ed. If a LA_ type language is called on lang(), it doesn't check to see if this is set.