[Решено] Translated slugs lead to 404 error

I have an issue on my main website bulgarimot.bg but the problem is also the same on my staging version which runs with bare minimum plugin:

Please use the staging version which has the exact same issue:

скрытая ссылка

When accessing the English version:

скрытая ссылка

It's a 404 error (Back to homepage).

The working page : скрытая ссылка

Should be скрытая ссылка ... as WPML understand it correctly.