The victorian-30s ones I have seen are all pocket-sized, with dense text split into numbered paragraphs with endless exercises of la plume de ma tante type, maybe with a page about how to do the joined up handwriting style of that country.
From the 50s-70s there seemed to be lots of medium sized books with continuing stories about families or tourists or whatever with dialogues for everyday situations, under a line illustration or a photo with the exercises based on the dialogue on following pages. The dialogues tend to be pretty stilted though. My favourite was a communist-era one I saw in Hungary that was basically stories about how life in England is pretty crap and depressing (through the life of a recently redundant plastic salesman who goes on depressing dates) in some sort of attempt to stop students wanting to visit.
The current fashion seems to be "here are some texts about ISSUES" on A4 pages with vocab about bicycles or whatever cunningly strewn about within the text and lots of little boxes and stock photos all over the page. There are some great examples, but also you get textbooks like one I have been landed with at work, sample discussion question "what is your most treasured carrier bag?"
What do you think the next fashion for mainstream language textbooks will be?