global_navtree is not defined on dutch page but is on other languages

  global, javascript, nav, undefined

I have limited knowledge (like it’s not my job) of HTML and no knowledge of JS.
I edit a website that was built years ago by somebody we hired but that person can’t edit the website anymore, that’s why I do it now.

I think I accidentally changed something in JS and now the navigation bar on top of the page is gone.

This is the website:

This is the English version where the navigation bar is still visible:

I can’t find what I did wrong!

Source: Ask Javascript Questions