Germany, Russia and Malaysia are three countries with national standards for fins/flippers:
DIN 7876. Tauchzubehör. Schwimmflossen. Maße, Anforderungen und Prüfung. Diving accessories for skin divers; Flippers, requirements and testing.
ГОСТ 22469-77. ЛАСТЫ РЕЗИНОВЫЕ ДЛЯ ПЛАВАНИЯ. Общие технические условия. Swimming rubber flippers. General specifications.
MS 974:2002. Malaysian Standard. Specification for rubber swimming fins.
The German and the Russian Standards use the word "flippers", not "fins", in the official English version of their titles. Only the Malaysian Standard uses the word "fins".
Furthermore, English is not the only language with two words for fins/flippers. For example, modern Greek has Πτερύγια-pterugia (fins) and Βατραχοπέδιλα-batrachopedila (frogfeet), while Brazilian Portuguese has nadadeiras (fins) and pé-de-pato (duckfeet). Both formal and informal words are used in both countries in diving equipment retail contexts.