Backoffice Product page tabs are not opening.

[Martino00]

When i try to open my products in the backoffice of my prestashop 1.6.1.23 only the first information tab is displayed.
I can't open any of the others.

In the developer tool i receive 2 error 

help.js:79 Uncaught ReferenceError: iso_user is not defined
    at HTMLDocument.<anonymous> (help.js:79)
    at j (jquery-1.11.0.min.js:2)
    at Object.fireWith [as resolveWith] (jquery-1.11.0.min.js:2)
    at Function.ready (jquery-1.11.0.min.js:2)
    at HTMLDocument.K (jquery-1.11.0.min.js:2)
VM3476:183 Uncaught ReferenceError: default_language is not defined
    at eval (eval at <anonymous> (jquery-1.11.0.min.js:2), <anonymous>:183:22)
    at eval (<anonymous>)
    at jquery-1.11.0.min.js:2
    at Function.globalEval (jquery-1.11.0.min.js:2)
    at e.fn.init.domManip (jquery-1.11.0.min.js:3)
    at e.fn.init.append (jquery-1.11.0.min.js:3)
    at e.fn.init.<anonymous> (jquery-1.11.0.min.js:3)
    at n.access (jquery-1.11.0.min.js:3)
    at e.fn.init.html (jquery-1.11.0.min.js:3)
    at Object.success (products.js:127)

2 days ago all was working good for the last year. And now suddenly?

I also can't enable or disable the cache.

Anyone a clue?