It‘s extremely simple. Several friends of mine have gone through the process and just had to do the language and society tests. Should not be an issue for someone who lived here for fifty years.

It's not. Plenty of people have done it.

What I’ve been hearing (which is admittedly not always reliable) is that Germany doesn’t like dual nationality, but seems to turn a blind eye in certain circumstances, one of which is the other country also being in the EU. That specific condition is causing a bit of angst in the few UK friends I have here in Berlin.

> Germany doesn’t like dual nationality, but seems to turn a blind eye in certain circumstances

Dual citizenship isn't a matter of "liking" but of treaties between the two countries. Some countries have it, some don't.

> special rules for EU citizens: They are not required to give up their previous citizenship in order to become naturalized German citizens, if their country of origin does not require Germans to give up their citizenship to become naturalized citizens of that country. [0]

[0] https://www.bmi.bund.de/SharedDocs/faqs/EN/themen/migration/...