Drupal Default Language Fallback
Multilingual menu's are quite nasty sometimes. I suppose you use i18n menu? Then have a look at the following:

Make sure the Menu link enabled only for the [LANGUAGE] language, on the menu tab of the node edit page is disabled. That makes sure the entry is shown on all pages. 

Also make sure the menu entry is language neutral by going to admin > structure > menu's > [MENU NAME] > [MENU ITEM] and check the language drop-down.