There are two ways in which you can translate wiki pages:
(1) using translation keys (with the localization script service). You keep
a single page and use the localization script service in the page title and
(2) using page translations as per
Currently the document tree displays the title of the default translation.
This means that you see translated titles only for pages that use the
localization script service in their title (1). Those that have translation
(2) appear with the title in the default language.
The title should be translated for both cases (1) and (2).