[2] He spent his first six years at the mission Eben-Ezer in the Western Cape, until 1848, when the family moved to Bethanie in Great Namaqualand (now South West Africa.
He spent many of his vacations at Schloss Poschwitz of the Privy Councillor Hans Conon von der Gabelentz, a colleague of Pott's, who owned an excellent collection of publications on Africa.
In 1871, he returned to SWA, settling among the ǁHawoben tribe of Nama (known by the colonials as Velskoendraers or Veldschoendragers, translating to "wearers of pelt shoes") in Keetmanshoop.
The immediate cause of the controversy was Hahn's written invitation to Transvaal Boer hunter Hendrik van Zyl and his associates in Ghansies to settle east of Rehoboth, in which Hahn told Van Zyl 40–50 settlers could easily take control of the area and alleged already inviting farmers from the Kamiesberg hills to settle in northern Namaland when he met them on a business trip to Cape Town.
The temperamental Hahn immediately appealed in a letter to the chief of the ǁKhauǀgoan (called by white settlers the Swartbooi Nama), who once had occupied the Basters' land, asking him to leave as well.
On the recommendation of the renowned German linguist Max Müller, Hahn was appointed on 1 February 1881, as the "royal philologist" and curator of the Sir George Grey Collection in what is now the National Library of South Africa campus in Cape Town, in which capacity he cataloged its contents as An index to the Grey collection in the South African public library (Cape Town, 1884).
He contributed heavily to the report of the 1883 Cape Government Commission on Native Laws and Customs, displaying his familiarity with the Nama way of life.
He gave valuable information on SWA's commercial potential to the young Heinrich Vogelsang, who was securing the first land concessions in SWA for the firm of Adolf Lüderitz, helping Vogelsang buy the Angra Pequena (now Lüderitz Bay) by recommending his bona fides to Josef Frederiks II, owner of that area and chief of the ǃAman Nama based in Bethanie.
The lean years in Stellenbosch yielded his brochure Viticulture in South Africa: a scheme for the development of the Cape wine industry (London, 1888).
Throughout 1889, Hahn worked in SWA as an agent for the Kharaskhoma Exploring and Prospecting Syndicate to acquire land and mineral rights to the territory of the Bondelswarts and the Velskoendraers along with the area of Swartmodder (now Keetmanshoop).
His conclusions and theories in Tsuni-ǁGoam, The Supreme Being of the Khoi-Khoi and On the Science of Language have not held up to scrutiny, especially in the latter, in which he reveals his antipathy toward what he called "the Dutch patois in this Colony."