The next upcoming English-language meetings in Hannover that I know of are:
Saturday, 28 April, 10 am
Children's reading hour
Escape Books & More, Oberstraße 8 (by Christuskirche in Nordstadt)
Usually a dozen kids and their parents, with both native and non-native speakers
(I might be there, probably not, though)
Monday, 30 April, 7:30 pm
Bayrische Botschaft (a.k.a. Paulaner), Thielenplatz
"SpeakEasy" -- usually 20-30 people, mostly non-native speakers, but some natives there
(I probably won't make it, but anyway)
Saturday, 5 May, 10 am
Children's reading hour
Escape Books & More
(I'll be there)
Saturday, 5 May, 6 pm
Anglican/Episcopal Holy Communion church service
Old Catholic parish hall, Brabeckstraße 24, Kirchrode
(I'll be there)
Wednesday, 9 May, 6:30 pm
Hannover Anglophiles
I *think* at the KDW, just off Osterstraße (they keep moving...)
Usually about a dozen people, mostly non-native speakers
(I should be there)
Wednesday, 16 May, 6:30 pm
Hannover4EnglishSpeakers (a.k.a. Whitney's Group)
Henry's Griddle, across from the opera on Georgstraße
Usually about 10-20 people, mostly native speakers
(I should be there)
If anyone knows of any others, feel free to add them.

Cheers,
Fairfax71