f17r

[-JKP-]

The horizontal line is enigmatic though. In German manuscripts, those are used with vowels as diacritics.

You can see the use of such a diacritic abbrev. mark (the horizontal line) to show the reader
 it concerns an abbrev. where (other and) many necc. letters have been lftt

(leftt=left out)

Yes, that's already been discussed above. The question is: was that common in German language manuscripts? Are there any characteristic examples?

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German documents were written with almost as many scribal abbreviations as Latin. Not quite as many, but most were adopted by one scribe or another.

The ones that were particularly prevalent in German documents were the Latin abbreviations for con-/cum- -rum/-orem -um/-us/-os re/er/ir con, per and pro. These, by the way, happen to match the characters in the VMS that were used for those abbreviations, as if the person who created the text wanted it to superficially look like they were Latin abbreviations.

What I mean are not "German documents", but documents in German language. Was there a similar abbreviation practice in place for the German language as it was there for Latin?

That's what I meant. I should have said, "Documents in German, French, Spanish, English, and Italian adopted Latin scribal abbreviations." They are full of them. You have to read them basically the same way.

Sometimes they used the sigla and other conventions for exactly the same meaning, sometimes, slight modification to adapt it to common letter combinations in that language (for example, Latin -us abbreviation might be used for -os in a language with different endings). In Spanish the c with a tail or the co ligature (which looks like a "w") is used for con. In Latin it's used for con and sometimes a few other things. All of them use Latin Per- abbreviation in exactly the same way (with the line across the p descender to indicate "er"). Same with Pro- and 4o (quarto).

Some were still writing whole books in Latin two centuries later, so there must still have been enough Latin readers out there to create a market for the books. A. Kircher's books from the mid-17th century, which found a wide audience, were written in Latin. Literate people  in the middle ages and Renaissance knew Latin and Latin scribal abbreviations and used those conventions when writing in their own languages. Some of the early typefaces made for printing books in the German language included Latin abbreviations.