Hi @adeliab,
Looking at your screenshot of the login page, it looks like you have the Classic Universal Login enabled instead of the New Universal Login. The tenant language settings will only affect the New Universal Login.
I see that you have the New Experience enabled on the settings page. Do you have the Customize Login Page enabled? If so, that will override the main settings and the Classic UL will be used.
Here is how to update the language using the lock widget if you’d prefer to stick with the classic experience: Lock Internationalization