In #907690-55: Breadcrumbs don't work for dynamic paths & local tasks #2, we changed the menu system to keep certain, untranslated links in a menu tree in order to get proper breadcrumbs.
I've forgotten the details about what caused us to keep certain untranslated links in the tree, and I apparently #failed to properly document the underlying reasoning in code (that's exactly why code comments should document WHY something is done, NOT THAT something is done).
All I remember is that it is required to make certain links to correctly appear in the breadcrumb. I hope that this is at least mentioned/documented somewhere in the issue summary or comments on it.
The block of code right above the "Skip links containing untranslated arguments" is related to that though, and likewise a block of code in menu_set_active_trail(), which is the only location that passes the $translate = TRUE argument to _menu_link_translate().
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