Cannot show translated text of Next button

Hi

The problem is that the next page button label is always Next and not the translated version.
Previous button works perfectly.

And even though it shows the translated label while debugging with form_alter function it is says "Next" in the button.

In $form_state variable there's a number of buttons such as next_button_text and first_button_text etc. which all have "Next" and Next().
I just don't remember anymore that which hook I used to debug form_state variable and in which I could see these buttons.

Yes, with preprocess_node() and r($vars) I can see following:

first_button_text	=>	Next
                                                function next
next_button_text	=>	Next
                                        function next