Hiding custom multilingual menu / doesn't function with blog posts

After adding a custom menu with multiple language options, for which it is important to add the language es / en / fr / de at the beginning of a URL. It doesn't seem to function completely, except for the English version. When navigating through the main navigation for Spanish/French/German website it seems to work: http://www.dametulengua.org/es/school, until entering into a blog post such as this one http://www.dametulengua.org/escuela-2/es/tallerconversacional. The top navigation titles suddenly changes to English (I have no idea why it changes to English out of all four languages).

How can I edit this?

Does it have to do with the page being a blog post of which I can't edit a custom URL?

Moreover, I can't seem to hide the menu in the top black part, due to custom code, is there a way to hide this?
This is because we get more mobile users, but the custom menu doesn't work for them so I manually added navigation in red text on all pages, to make it work on mobile. However on the desktop version, this leads to both the menu in the black header and the red added text menu showing up.

Thank you in advance.
 

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