Do you have a version of the page translated into the the selected culture? For any page of your content tree you want in multiple cultures, you have to create a version for each culture. If there isn't a translated page for the selected culture it will redirect tot he default site culture.
Using the default language version for untranslated pages
You can configure websites to display content from the default language for pages that are not available in the selected language.
In the Kentico administration interface, open the Settings application.
Select the Content category.
Choose your Site enable the Combine with default culture setting.