Q: Incorrect Language when creating books in Photos

Is that the standard Lorem Ipsum placeholder?  If so, you just replace it with your own text.

https://en.wikipedia.org/wiki/Lorem_ipsum

The placeholder text will not show in the finished book.  It is just used to give you an idea, what the page will look like, when you insert the text.

You cannot change the size of the textfields in Photos for Mac photo books, so it is important to pick a page layout in advance that has a textfield large enough for the text you want to insert.