Two elderly men thought to be the last speakers of a Latin American language are refusing to speak to each other.

They are in their seventies now and should be doing their bit to pass their language on to other people in their community.

But a Mexican institute says it is concerned that their rare language may never be heard again.

The two old men who aren't talking live in the Mexican state of Tabasco and their mother tongue is an indigenous language called Zoque from Tabasco.

Fernando Nava is a linguist and knows the pair.

"They don't speak to each other by personal reasons, nothing to do with the language itself," he said.

"They have a personal story. One of them is a prosperous man, the other one is a poor man."

Mr Nava works at the Mexican Institute of Indigenous Language and he says the institute is trying to encourage family members to learn Zoque from Tabasco.

"We hope one of their families will take more interest," he said.

But the institute is up against an old obstacle. Many people would like to learn another language but don't always follow through.

"They say in front of you, they say, 'It's nice, our grandfather is very important people', but it's difficult to have a persistent problem to get new speakers of the language."

In 1960, according to a Mexican Government survey, there were 367 speakers of Zoque from Tabasco. In the early 1970s, linguists could only find 40 people who spoke the language.

And now there are apparently only two: grumpy old men.

Indigenous languages are disappearing at a steady rate. The United Nations organisation UNESCO (United Nations Educational, Scientific and Cultural Organisation) estimates that half the languages in the world today could be lost within "a few generations".

Dr Paul Sidwell works to save endangered languages. He is a visiting fellow at the Australian National University's Research School of Pacific and Asian Studies.

"The first thing to do is to record the language, to document it in as far as we can, in all the different ways it's used, document the lexicon, the grammar," he said.

"Once we have a description of the language, then we know what it is we're trying to preserve."

Dr Sidwell says if the men refuse to speak to one another, there may be other ways to save the language.

"The first thing I would tell them is to write things down, to document in writing their knowledge of the language if we can't actually record them speaking," he said.

"So, if they're writing down recollections, stories, folktales, recollections of conversations, then at least they're maintaining their use of the language and we have the benefit of the permanent record that emerges from that writing.

"And then maybe their attitude will warm up a bit to speaking again."

- ABC/BBC