There is no requirement for a tower ATCO here in the UK either.
So where's the issue then? Obviously the airfield needs AFIS and some coordination with ATC (= a telephone + computer). In Germany, small airfield instrument procedures are a very rare thing but it is possible. The way they do it today is via an airspace F, that is essentially uncontrolled airspace like G but with higher minima and with IFR allowed (Germany does not allow IFR in G, if that was to be changed, F would not be necessary at all). ATC vector you onto final and once you descend below their minimum radar vector altitude (or get close to airspace F), they will tell you "radar service terminated, contact XYZ Info on 123.45". AFIS will in turn inform the others: "to all stations, airspace foxtrot active, IFR traffic on 5NM final runway 25". That will tell everybody that circling below a cloud east of the runway is not a good thing to do for the moment.
I have also encountered airfields without instrument procedures here that are hooked up to the ATC network and can issue IFR clearances for Z flight plans. They usually have it when they're close to a big airport.
Examples of this are EDTY Schwäbisch Hall (ILS+RNAV) and EDMS Straubing (RNAV). Both are uncontrolled airfields with AFIS.