Linguistic distance is a concept that seeks to measure the degree of difference between two languages. Since the linguistic distances between languages are as different and variable as the languages themselves, such a concept cannot be accurately applied in a scientifically precise manner. This concept is important due to the increase in globalization, which has led to international trade between business concerns from different countries with different languages and dialects. It is also relevant as a tool to measure the ability of immigrants learning a new language that is different from their mother tongue. This is because the more removed one language is from another, the more difficult it will be for the immigrant to adapt to the new language.
Linguistic distance can be measured by measuring the mutual intelligibility of the language to the speakers. Mutual intelligibility determines how easy or difficult it will be for the speakers to grasp the fundamentals of the new language. This may be facilitated by the sharing of some common words or the similarity in the arrangement of grammatical and lexical forms. For instance, different territories or countries may speak the same basic language with only some minor or major differences in intonation, meaning of words, and the application of the language in general.
American and British English, for example, are mostly related with only a few easily surmountable variations. The linguistic distance between the methods of speaking the language is very small. On the other hand, Irish brogue and Cockney accent might prove to be a greater challenge for an American listener even though they are still variations of the same language. For these, the linguistic distance is more than that of British English. Even at that, learning to understand and speak these versions of the English language would not be as challenging as learning to speak Russian, since both versions are more related to American English and have a higher measure of mutual intelligibility.
The ability to easily overcome the linguistic distance between two languages is easier for children below the age of seven than it is for adults. This is due to the fact that there is a threshold in which children are still open to absorbing the fundamentals of speech patterns without encumbrance from other learned languages. Children below seven are still able to assimilate the fundamentals of a new language, master it, and speak the language without an accent better than adults. This effect can be observed in new immigrants to a country with a different language. The adults may eventually learn the new language, but the possibility of retaining accents carried over from the mother tongue is very high, especially if the linguistic distance is high.