As Germany is a western industrial nation with a high standard of living, all caves are well developed and secure. Several institutions, like the TÜV (Technischer Überwachungsverein, technical surveillance institution) and the Bergamt (mining authority), make sure all public sites are save for the visitors. Nearly all caves and mines are easy to access with little need to walk. The last show cave with carbide lamps was modernized with electric light several years ago (unfortunately). Mines typically offer helmets and some kind of overcoat.
Germans like to travel themselves, most of them speak, or at least understand, some English. On the other hand the German sights are not used to foreign visitors. They are primarly visited by German day trippers or groups like school classes or company trips. American and Japanese tourists tend to accumulate at a few spots (Oktoberfest, Neuschwanstein, Heidelberg and Christkindlesmarkt). At other locations they are rather rare, and so it is difficult to get a tour in a foreign language. Only very few caves offer them, typically only after appointment. Some caves provide written translations.
Most German caves and Mines are maintained by a Verein, a non-profit (caving) club, where most of the work is done by volunteers. This reduces cost and is the reason why entrance fees in Germany are lower than in most other Western European countries. But the quality of the cave tour depends much on the respective guide, typically also a volunteer. Most of the sights have very good booklets on a high scientific level, unfortunately again only in German. Photography is allowed in most caves and mines, but there are regional differences.
Nearly all caves and mines in Germany are closed during Winter. The often told reason is to protect bats, but another good reason is the lack of visitors in winter. The caves of the former German Democratic Republic (DDR) were maintained by the socialist state, who paid the guides all year. This happened to be impossible under the new capitalistic system. So they changed their open hours too.
Several caves are open in winter to groups by appointment. This is not mentioned on this site, as it is a basic fact. So if you think about visiting a cave in winter it is always worth to contact the administrator.