I suspect that the actual text of the button isn't just "Weiter >"
but also includes an &
in there, for the accelerator key. Try pressing Alt
and see if a letter appears with an undescore under it. If it does, then that letter is prefixed with an &
.
This "solution" is actually pretty flimsy though and could easily break. For example, what if the user has another language configured on their system?
It is possible to get the ID of the button, which would be unlikely to change. But you would first have to find the installer window and then enumerate its child windows. To find the ID of the button, use Spy++ as JosephH suggested in his comment.