Why are some of the texts in English?

You can change the language under "Settings", but if you find that the texts are in English even though you have changed it to something else when you click around in Biblio, it is most likely because there is a setting in your browser or on your computer that needs to be changed.

Therefore, check the language settings and translation in your browser and/or on your computer.
Some computers are set to 1) default to perceive all pages as English and 2) machine translate English.

When this is changed, the texts will also change inside Biblio.