When Kevin Rosenzweig's best friend died four years ago, he lost more much than a companion: he lost his language.

"I still miss my friend Gordie Seidel from here," Mr Rosenzweig said, standing next to his mate's polished granite headstone.

"He was the last one that I could freely speak German with."

Mr Rosenzweig and Mr Seidel spoke a unique kind of German, known as Barossa Deutsch.

Sprachinsel - 'Speaking islands' Although the term 'sprachinsel' is German, linguists use it to describe any language that exists as an island amongst a dominant language group. For example, there's a Dutch sprachinsel in Canada and a Croatian one in the Italian city of Molise. Barossa Deutsch isn't the only German language island either. Professor Peter Mickan says there are extensive German sprachinseln (the plural of the term) throughout South America. He says in the United States, Texas German and Pennsylvanian German have been widely studied. Remarkably, German sprachinseln existed (and still do today) in the former USSR, through the Volga region and in Kazakhstan.

Linguist Professor Peter Mickan explains the language evolved in South Australia's Barossa Valley amongst the early settlers.

"They came from central Europe by and large in an area now that borders across into Poland and into what used to be East Germany," Professor Mickan said.

"By 1850, 1860, one in 10 people in South Australia were of German background."

They formed an island of German speakers, set in a wider ocean of English.

Professor Mickan said linguists have a term describing such a situation — fittingly, it's German.

"A sprachinsel is the technical term we use in linguistics," Professor Mickan said.

"So a sprachinsel is a little island where a language is spoken and is maintained over a long period of time."

As Charles Darwin discovered in The Galapagos Islands, around about the same time the Germans were heading to South Australia, isolated things evolve in interesting ways.

Early German settlers in the Barossa Valley outside a house. ( Supplied: State Library of South Australia )

It's not just lizards and finches, the same happens to a language.

"One of the things that happens is to the grammar," Professor Mickan said.

"The grammar will change as the speakers need to communicate with the local community, and it was an English-speaking community, they adopt some of the English grammar and then incorporate the German and the English.

"The language also doesn't keep up with technical terms.

"When my parents were in Germany in the 1970s, people asked how they got there, they replied 'luftschiff' — an airship. They didn't know the term, 'flugzeug'— an aeroplane.

Outbreak of war put German communities under scrutiny

During both World War I and World War II, the German 'speaking islands' came under attack.

Sorry, this video has expired Sir Hans Heysen painting.

Authorities were extremely suspicious of those communities, doubting their loyalty.

German language schools and newspapers were banned. Thousands were interned, or deported.

Not even a famous name offered a shield, if it were German in origin.

Earlier this month the ABC revealed police kept renowned landscape artist Hans Heysen under constant surveillance, despite abundant evidence of his loyalty to this country.

All of this makes Mr Rosenzweig's story all the more intriguing.

He started school on the eve of WWII.

A friend at Towitta Primary School translated for Mr Rosenzweig during class. ( Supplied: State Library of South Australia )

Despite authorities' best efforts to stamp out German, Mr Rosenzweig knew only one language on his first day.

"I didn't know no English," Mr Rosenzweig said.

"When I got there the teacher, well he started talking and I think I said, 'Was? ... Was sprecht du? [What? What are you saying?]' I didn't know what he was talking about!"

"My friend Coral Rothe, she knew both German and English, so she translated for me and that's how I got started."

Language needs to be spoken to survive

Part of Professor Mickan's work has been interviewing remaining speakers of Barossa Deutsche, documenting their experience.

Early German settlers evolved their language amongst English speakers. ( Supplied: State Library of South Australia )

At the Sedan pub, near Mr Rosenzweig's home, the pair sit down for a chat over a beer.

They talk about Mr Rosenzweig's family — did they speak only German at home? Did his family still use horses on the farm when he was young? Does he remember their first tractor?

To assess language ability and see how it varies from the standard, linguists usually present people with lists, asking, for example, what's the word for hand or foot?

Professor Mickan argues his approach, apart from being much more interesting, gives a clearer insight into people's abilities.

"The German community [here] has been separated from Germany for over 160 years and the interesting thing is that Kevin is able to conduct a full conversation with me in German across a range of subjects," Professor Mickan said.

Putting down his beer, Mr Rosenzweig replies, "I don't think I'm very good, but thank you".

The exchange illustrates an important point: language needs to be spoken or it dies.

German over kaffee und kuchen

The other significant part of Professor Mickan's work has been to establish a 'kaffee und kuchen' group (or 'coffee and cake' in English).

"Speaking with the older generation, the one thing they really missed was chance to speak the language in an informal group ... to just chat," Professor Mickan said.

"For the Barossa Valley it's a rehabilitation of people and their identity and their culture."

Gordie Seidel's grave ( ABC News: Simon Royal )

Once a month German speakers in the Valley meet at Langmeil Church in Tanunda.

They drink coffee and eat cake. And, of course, speak German.

The group's been going for two years but a few days before his pub interview with Professor Mickan, Mr Rosenzweig went to his first kaffee und kuchen.

He still misses Gordie, but at last he has found some new friends who speak his language.