I was talking to fabie about this on IRC, and I had the same problem
with a recent site. The reason for the problem is sort of a catch-22 -
you can't translate the page because you can't see, because it doesn't
have a translated version yet. The current code breaks this rule for
root-level pages (those with ParentID = 0) so that the first level
always appears, but doesn't seem to have any children. The workaround
right now is to switch to the default language, find the page you want
to translate (e.g. a second-level page), then create a new translation
from the dropdown under the Translations tab. Once you've created the
translation and saved it, the next refresh of that tree should show the
child page when in the translating language.
Ingo and I had a crack at fixing it a while back, but time was tight on
the project and it was the day before launch, so we ended up not quite
polishing it off, I might try and dig out the code and patch the latest
2.2.2 if I have some spare time.
Hopefully that at least helps as a workaround until the issue is patched.
Matt.