Multi-level navigation and easy menu definition

[yojoe]

Does anyone have an idea how to display a menu tree containing slugs of defined page, where slugs also have nested pages, but slugs on lowest levels shouldn't be opened until visitor clicks on their parents.
Structure I have contains top lvl pages, where a certain page (call it page1) has more nested pages inside, and they have another siblings (3 lvl menu)
index
page1
|- subpage1
subpage1sibling1
|-- subpage1sibling2
|-- subpage1sibling3
|-subpage2
|-- subpage2sibling1
|-- subpage2sibling2
|-- subpage2sibling3
|-subpage3
|-- siblings
...
page2
page3
etc.

I'm trying to show on all pages a menu consisting of page's1 1st level siblings:
|-subpage1
|-subpage2
|-subpage3
When visitor clicks on subpage1, its siblings should be shown along with siblings of page1 (parent).
|-subpage1
|-- subpage1sibling1
|-- subpage1sibling2
|-- subpage1sibling3
|-subpage2
|-subpage2
|-subpage2

Can't find the way to display needed data using return_i18n_menu_data function.
Maybe there's another way of displaying such menu structure and navigation ?