Irish charity walkers speak ISL in China. John Cradden reports.

How can a group of Irish people, who speak no Chinese and have no interpreter, communicate with Chinese people who speak no English? After their five-day, 100-mile walk along the Great Wall of China to raise money for an Irish charity, 14 Irish people are meeting up this weekend with a group of Chinese people.

The walk along the Great Wall sounds like a challenge enough, never mind any attempt at fluent conversation. Yet far from facing a Great Wall against communication, fluent exchanges are likely to be struck up between members of both groups within an hour. How will this be possible?

The charity walk is to raise money for the Irish Deaf Society. One of the participants is Alvean Jones, a presenter of RTÉ TV's deaf community programme Hands On.

The answer to the riddle lies in a system of communication called International Sign Language (ISL). This is not a language in the same way that Irish Sign Language or Swedish Sign Language is, she says. "It's a mechanism for finding common ground between two different sign languages."

According to Prof Bencie Woll, of City University in London, deaf people use up to 70 percent of the vocabulary from their own sign language when interacting in international situations with people who use a different sign language. In addition, they use a lot of the grammar structure from their own sign languages, according to Lorraine Leeson, director of the Centre of Deaf Studies at Trinity College, Dublin.

What this all means is that International Sign Language is not the kind of thing you can systematically learn like a second language.

"You have to think of International Sign as a medium of communication for short-term events rather than as a way in to learning a language of another deaf community, said Leeson. Similarly, there are no interpreters for ISL. In situations where ISL is being used, interpreters will be improvising rather than translating.

Leeson believes the encounter between the Irish and the Chinese deaf people will be very interesting. "There may not be that many shared international references to work from but there will be the shared experience of deafness that the two groups will have in common.

"If deaf people go abroad and see a person signing, there's an automatic contact. The first thing someone will say to you is "Are you deaf?" And what they mean is "Are you one of us?" I think that's where the conversation will flow very well."