It is possible for the login page to be in a different language than the language you selected for your platform.
I have configured my platform in French, yet my login page is in English.
This is possible because the login page's display is based on the browser's language settings.
I have configured my platform in French, and my browser is set to French, yet my login page is in English.
The browser may be set to French (menus are displayed in French), but it may still be configured in such a way that English is given priority.
For Chrome, this setting can be verified at this address: chrome://settings/languages.
You can see below that French will take precedence over English.