I walked from Prague to Nuremberg last year using the Tillyschantz route and from Nuremberg to Einsiedeln in Switzerland this year; both walks were about 4 weeks. The gps tracks from Peter Robbins, together with the published route description in German and the usually good waymarks, was adequate for wayfinding. I am somewhat conversational in German but not in Czech (a Slavic language with no resemblence to English whatsoever, very tough to learn, even the basic politeness phrases). Supplies are tough to come by outside the very big towns, so one needs to carry supplies for several days at a time. The further west you go, towards the German border, the rougher the country becomes. I started from Prague the middle of May; and found I was the only walker that week! Along the route, neither English nor German is reliably spoken; you are truly in for a pilgrim experience, relying on the kindness of strangers. The scenery and views are lovely. The evening meals are substantial, but breakfast is a hit-or-miss proposition. Very rare to find churches that are intact and open; many buildings were saved but converted to other uses.
The day after Zviekovec, I lost the track, took a couple of severe falls down a steep ravine, and needed assistance. (Details in the blog.) The Czech couple who rescued me and tended my injuries were jewels!
The section in Germany is much more benign, with more reliable availability of supplies, and also more expensive. So in summary, the route from Prague to Konstanz covers a wide variety of terrain; it is a very different experience from walking in France or Spain; the guidebooks available are in German, so speaking and reading basic German will be helpful; the waymarking is decent but gps tracks as a supplement are very helpful; May has good weather but very few walkers - the numbers increase a bit in June, with July and August being very popular for walking.