8 – Link of the main menu as a language changer

I have 2 languages ​​and these situations:

main menu -> lang1 -> link to www.foo.com/
Main menu -> lang2 -> link to www.foo.com/en

All sites work if they are changed manually in the browser … but my main menu link does not work.

I do not have space to place another block with the menu switch in the main menu bar.

I hope someone can send me in the right direction because I spent 8 hours without solving these problems.