Broadly speaking, Localisation is a process of adapting product or service to a local condition. Localisation as a process appeared only several decades ago, before that time most of the business was local in nature. Transportation and communication costs were prohibitive, so most products were made locally. Of cause books, scientific papers and drawing were transported from one country to another, but it was not as widespread as now.
Only one hundred years ago it took almost a month to reach New York from London, on Concorde you can do it in four hours. In western countries there is almost no distinction between local and international calls, cost are miniscule for both. So one products are sold worldwide and have to be adopted, i.e. localised, worldwide.
Localisation is not a simple process. People in different countries not only speak different languages, they also have different customs. Localisation means that product or service should not differentiate from product made up and produced in local conditions.