In 1962 Lang became lecturer in Geobotany at the University of Karlsruhe and in 1966 he submitted his habilitation thesis on the macrophyte vegetation of Lake Constance.
Lang travelled widely as part of his research and botanical activities, including visits to the French Massif Central in 1956; Botany School Cambridge, UK in 1959; the Australian Alps and Australian National University, Canberra in 1965; Siberia in 1971; Armenia in 1975; western Canada and western USA in 1978; tropical and central Australia in 1981; and Argentina in 1983.
During his time in Karlsruhe, Lang’s research focus lay on vegetation mapping at the scale of 1:25,000 based on classical plant sociological relevés of the Upper Rhine Plain, the Black Forest, and the Lake Constance region as well as the study of lake and mire deposits with regard to the vegetation history of south-western Germany.
During his time in Bern his research centred on the Alpine region with special reference to the study of dynamic vegetation processes and climate change in the past, as well as the development of multi-proxy approaches in palaeoecology.
He introduced new equipment and methodologies, especially with regard to subaquatic coring from a raft that allowed sediment sampling from the centre of lakes, which provided new insights into local and regional reconstructions of past environmental conditions.