There is a fundamental linkage between language and traditional knowledge related to biodiversity. As languages go extinct, there is an irrecoverable loss of unique cultural, historical and ecological knowledge. Local and indigenous communities have elaborated complex classification systems for the natural world, reflecting a deep understanding of local flora, fauna, ecological relations and ecosystem dynamics. This traditional ecological knowledge is both expressed and transmitted through the local or indigenous language. When young people no longer learn the language of their ancestors, special knowledge is often lost, as it is not transferred into the dominant language that replaces it. This is often because the dominant language does not have the vocabulary for this special knowledge, or even because the very situations in which this kind of knowledge and its relevance for survival are learned do not occur in the dominant culture. Information on status and trends of numbers of speakers of indigenous languages may therefore be used as a proxy for measuring trends in the status of traditional knowledge, innovations and practices.
 
There are estimated to be 5,000 to 7,000 languages spoken today. Some 250 languages in total are spoken by 97% of the world’s people, while the remainder are spoken by around 3% of the global population. More than half the world’s languages are believed to be spoken by fewer than 10,000 people. Over 80% of these minority languages are confined to a single country. The geographical distribution of languages, like the distribution of biodiversity, is very uneven, with some parts of the world having far more languages per speaker than is the average, reaching its peak in the island of New Guinea.
 
For the indicator on the status and trends of linguistic diversity and numbers of speakers of indigenous languages, data will largely be available at national and regional scales, and by 2010 it is expected that the basis for estimating trends will most likely be regional case studies.
The CBD AdHoc Technical Expert Group (AHTEG) on Indicators noted that data on the status of linguistic diversity and numbers of speakers of indigenous languages are available through the Ethnologue database. However, a methodology for the extraction of meaningful trends information from these data is yet to be developed. An index on the number of indigenous languages losing speakers versus indigenous languages gaining speakers might be feasible and could be a more sensitive indicator of the actual status of indigenous languages, rather than a simple count of languages in each category of numbers of speakers.