As I was looking at an older volume of the De Boor/Newald Geschichte der deutschen Literatur, I came across a claim for the percentage of German-language printing that struck me as a bit off. Now that we have some better data from GW/ISTC, VD16, and VD17 to work with, it should be possible to compare German and Latin printing across two and a half centuries, from 1450 to 1700 - at least with a few caveats. For incunables, I'm including only what the ISTC assigns to the region of Germany. VD16 doesn't include broadsides, so for the sake of consistency we should exclude broadsides from the incunables and seventeenth-century books as well, as the percentage of vernacular broadsides can be surprisingly high at times. Also, VD16 only includes language data for not quite half of its titles, so we'll have to compare percentages rather than title counts, and hope that VD16 has provided language data for a reasonably random sample. We also have to keep in mind that VD16 indexes every title in a volume separately, so one volume including multiple titles will be counted multiple times - which is less of a concern, as we're interested in the overall percentage. Finally, we're ignoring bilingual works.
Here's the graph:
What we find for 1480-1600 is not substantially different than what you can find in Uwe Neddermeyer's Von der Handschrift zum gedruckten Buch (2:698, diagram 12a, Reich/nationalsprachlich), although I find the longer time frame of my graph helpful. Vernacular printing declines after the 1480s, experiences a sharp rise at the time of the reformation, then settles into a slow decline that lasts until the outbreak of the Thirty Years' War. The amount of change between 1530 and 1700 is really quite modest, however.