Localization (L10n) is the process of translating software user interfaces from one language to another and adapting it to suit a foreign culture. These resources are for anyone with an interest in the technical aspects involved in localization. They are for developers and all contributors.

The documentation here is no longer being maintained and is inaccurate. L10n documentation has moved to https://mozilla-l10n.github.io/localizer-documentation/ . To learn how to bootstrap a new locale for Mozilla projects, please see those documents

See also

Localizing MDN
This resource covers localization of the documentation here on MDN.
App localization
This set of documents applies more specifically to localizing apps, including Firefox OS apps.
Reference docs for the L10n API that Mozilla uses to localise Firefox OS.