The German Statistics Authority (Statistisches Bundesamt) released the 2019 citizenship figures on 3rd June 2019.
You can read the press release below in German and English. The headline figures are that the largest number of British citizens were naturalised in 2019 (14600), which was more than double that of 2018 (6600). Since the Brexit referendum in June 2016, 31600 British nationals have been granted German citizenship.
These numbers are unprecedented in British German history. They present a large shift in social and citizen identity for around a third of British citizens living in Germany, the large majority of whom will have chosen to keep their British citizenship. At present application for dual citizenship is possible until December 31 2020 after which you may be asked to give up your British non-EU citizenship in order to be granted German citizenship. **Note, application and not decision on application.
Prior to the Brexit referendum, the annual naturalisation numbers were a few hundred each year: 2015 – 600, 2014 – 500, 2013 – 500, 2012 – 300, 2011 – 300
Below some British media reports on the numbers:
The Times: (firewalled)