My 2 cents:

Germany

TL;DR

Germany is a great country to visit by bike, there are lot's of camping places, various landscapes and great bike lanes pretty much everywhere. I particularly recommend Berlin to Lubeck, via Rostock, I really enjoyed riding by the Baltic sea (Ost See).

Signs

There are many road signs for bike, most of them are green and lead you to roads that are either fully separated from cars or have low traffic.

Travel app

I'm a big fan of https://cycle.travel/map. we usually build our routes in there, download the GPX file, upload it to komoot and then to the GPS, but if you are riding with your phone, there is navigation included in the cycle.travel app.

Trains

Almost every regional train (Regionalbahn, RB) and S-Bahn (suburb train) have at least one bicycle friendly car. You may need to buy a ticket depending on the company managing the local transports. For example in the trains of RMV around Frankfurt, Mainz, Darmstadt, no need for a ticket, but around Köln, you will need one (if I remember correctly). In small train station, there is often no elevator, be prepared to carry your bike on stairs. I would highly recommend not planning to take a regional train on a Sunday or a public holiday (which vary depending on the state/Bundesland), because Germans love their Sunday's hiking trip but the trains are smaller and less frequent on these days, so you might not even be able to enter the train with you bike and luggage (happened to us). It's also possible to take long distance train, IC (slow) and ICE, but you better book in advance as the places are very limited. Also, don't hesitate to ask people to move away from the foldable sits, if you don't say anything and just awkwardly stay in the middle of the way, they will look at you suffer for the whole trip holding your bike and moving it around to people go in and out, without ever suggesting to give you the space (again, happened to us). Instead, promptly ask for it, these are places made for bikes and stollers, unless the train is full, there is no reason to lock these places for other reasons.

Camping

As far as I know camping outside of regulated camping places is forbidden, I would not do it unless I have no other choice. Also it's fairly cheap (often under 15€) to have a place for a tent and two bikes in a camp site, plus it's nice to have commodities accessible IMO. For the stove, you will easily find gas from Primus or Camping gas in Germany.

Our favourites routes are:

• Romantischer Rhein: approximately between Mainz and Bonn, great landscape, to do especially if you like wine.
• The Mosel river, from Koblenz (DE) to Metz (FR).
• Baltic coast, the best camping in all Germany are there IMO. I also enjoyed the lakes around Leipzig, the forests in Brandenburg, the Elbe around the beautiful Dresden and everything in between. BTW, if you are around Dresden, I also recommend letting the bike aside for a day or two to hike in the Sächsische Schweiz, in particular to tour the Malerweg (the way of the painters): truly beautiful.

Supply

You should not have any issues finding supermarket, you will have a lot a choice in REWE, EDEKA or Tegut, organic stuff in Alnatura or Denn's and cheap stuff in Lidl or Aldi. On Sundays, Germany is either hiking or having a Frühstuck, you wont find many shops and restaurant opened., I recommend resupplying on Saturday. However, when it's sunny make a pit stop in a typical Biergarten, fresh beer and snacks to keep you going. Also, it's very easy to get vegetarian/vegan food in Germany, which is nice.

Language

As a foreigner leaving in Germany, it's really hard finding Germans that do not speak English. Nowadays, I'm really trying to speak only German, but I know I could switch to English in most cases. They will appreciate if you can say Hallo, Tschuss and Danke and they will surely tell you your German is very good even if you can't say anything else. Bonus point if you can say "Ich spreche nicht Deutsch, spechen Sie English?".