The process of adapting a web application to run in more than one language is variously referred to as localization or internationalization.
Recently I was asked to compile a list of all CiviCRM releases since 3.1.0, identifying which were security releases so that we could make sure clients' sites were secure. The organization I work for (Freeform Solutions) is focused on doing sites for other non-profit organizations, many of whom are still running older versions of CiviCRM due to budgetary or other constraints, so we wanted to be sure that no one was running a version known to contain security vulnerabilities.
The attached chart came out of a discussion between Kasia Wakarecy, Lola Slade and myself (Lynna Landstreet), at Freeform Solutions, about some issues we'd encountered when trying to to do major version upgrades of CiviCRM and Drupal on a client's site at the same time. Since we're likely to have a number of other combined upgrades like that to do in the future, we wanted to iron out the best process for doing them as smoothly as possible.