Born in the southern town of Cradock in 1936, the mixed race activist would go on to campaign against apartheid in the 1950s and spend a decade on Robben Island.
Alexander obtained his doctorate in German at the University of Tuebingen in then West Germany in 1961.
Three years later he was convicted for conspiracy to commit sabotage in South Africa against the white minority regime, along with other members of the National Liberation Front, which he co-founded. He spent the next 10 years on Robben Island, a political prison off the coast of Cape Town.
One of Alexander’s companions was Nelson Mandela, who spent 27 years in various jails before he was released and became South Africa’s first black president in 1994.
Alexander taught other inmates history, while Mandela taught law and current presidential spokesman Mac Maharaj economics.
Released in 1974, the scholar joined Steve Biko’s Black Consciousness Movement.
Alexander ran in the 1994 elections at the end of white minority rule with the Trotskyist Workers Organisation for Socialist Action, which won 0.02 percent in the poll.
Having joined the University of Cape Town, Alexander later focused on multilingualism in a nation discovering democracy and confronted with the increasing influence of English.
South Africa has 11 official languages, but English is often used as common language.
“He will always be remembered for his pioneering work on language policy, including his most recent work, focusing on the tension between multilingualism and the hegemony of the English language in the public sphere,” said President Jacob Zuma in a statement.
“At a professional level, Dr Alexander, as an accomplished linguist, contributed immensely to language development in our country,” Zuma added.