Translated menu does not appear

Hi everyone,

I have already used I18n a few months ago without any problem, but now i don't understand what's happening...
I want to add an English translation to my website.
I can translate the pages (translate tab is there), but when i switch languages the translated menu items do not appear, the only thing that is present in the menu is my contact link....
And the language switcher block is not working well too when i am on my frontpage, nothing happens.
I also sometimes encounter the problem of a not found page...

Has anyone experienced something like that before ??

Thanks a lot