- Best thing to start is probably Sofie Beier’s Type Tricks. Her Reading Letters is to an intro to type design but to legibility research, and has proven very useful for (advanced) type design.
- @Martina_Flor’s book is about Lettering, but has a lot in to that is useful for getting started in type design.
- Thomas Maier wrote a handy book in German, Fonts formen.
- @Laura_Meseguer’s and @TypeTogether’s book is not available in German
- Gerard Unger wrote a few books, I translated one in German, Wie man’s liest. Spare copies available through the tga.
And one day, I will convert my handouts into a book, though I have been saying that for years now already. I can send you the German version of the PDF if you like.
Contact me on DM, also if you want Thomas Maier’s and the German translation of Gerard Unger’s book. I’ll hook you up with the right people.