What it says:
81 - 1029 -4
FLOATING
MADE IN HUNGARY
42 - 43
SIZE - 8-9
DIN 7876-a
FL 255
FB. 95
As a vintage equipment snorkeller, let me say how delighted I am to have something vintage other than breathing equipment to discuss in this forum!
The DIN 7876-a inscription I can identify because I have a copy of German Standard (DIN="Deutsches Institut für Normung") 7876 of October 1980. The title of the Standard in German is "Tauchzubehör; Schwimmflossen, Maße, Anforderungen und Prüfung", with "Diving accessories for skin divers; Flippers, dimensions, requirements and testing" as the official English translation. The Standard is mainly about the sizing of swim fins, specifying which foot length should go with which foot width. Two other countries have similar Standards, Russia and Malaysia, for fins. The Malaysian Standard MS 974 is partially based on the German Standard DIN 7876. The "a" appended to the Standard number 7876 identifies the fin as being "Form A", a full-foot design, or "Schuhflosse" (shoe fin) as it is called in German, while "Form B" serves to identify a heelstrap fin (German: Fersenbandflosse).
So I conclude from the data on the back of the fins that they date from October 1980 or later.
A postcript. I've just had a rummage among my vintage fin collection and located a pair of Dolfino Marina Pro rubber full-foot fins which I purchased via eBay. I haven't used them as they're too narrow-fitting, despite being my size in terms of foot length. They look identical to yours, same concave fin tips, same wavy heel pattern. On the reverse side I have a similar series of inscriptions:
MADE IN ITALY
FLOATING
81-1035-81
46 - 48
SIZE-11-13
DIN 7876-A
FL. 275
FB. 105
I'm guessing that the FL and FB refer to Fußlänge (foot length) and Fußbreite (foot width) respectively. Ironically, DIN 7876-A states that for foot length 275 mm, the corresponding foot width should be 110-115 mm, so my fins don't qualify for DIN 7876-A endorsement. No wonder I find the fins too narrow-fitting! In the case of your fins, foot length and width match the German Standard, which prescribes that a foot length of 255 mm should go with a foot width of 95-105 mm.
Interesting that your fins are made in Hungary, while mine are made in Italy. I expect the manufacturers of Dolfino Marina fins had their products made wherever it was easiest or cheapest to do so. In the 1980s, Hungary was still in the communist bloc of East European countries and would likely have had lower labour costs than Italy. Full foot rubber fins are still manufactured in Hungary nowadays:
