Difficult to fololow you description of what you have done and exactly what you have done:
edited
msql to change page4 to Size Chart
Try not to make this harder than required....roll back to a standard install if you can and then start by only entering your information through the defines page editor for page_4...mostly to verify that what you are entering is working. When this is functioning correctly and content is displaying as you want, edit the includes/languages/english.php and find:
Code:
define('BOX_INFORMATION_PAGE_4', 'Page 4');
and change to
define('BOX_INFORMATION_PAGE_4', 'Size Chart');
Now this will get the display as you want and then only if you need to browser descriptions to match also should you go into this. But basically doing this will validate that you have content that displays correctly.