Integrated application localization techniques are described in which support for application localization is provided as an integrated component of a development environment. Localizations for selected languages/locales integrate with application builds in the development environment so that updates are synchronized with project resources for multiple languages. This involves creating and employing localization files corresponding to source content of a project using a designated file format suitable to enable translations. Localization files that are created in the designated format may be exposed in various ways for translation via the system, a developer, a translation service, or other selected translation sources. A single multilingual resource file for an application is then generated to contain resources in multiple languages based on translations made available through the translation sources.