A method, computer system and computer program product localize a source language user interface of software application to a target language user interface. While the software application is executing using the source language user interface, source language GUI component text of a GUI component is extracted from bytecode of the software application. The extracted source language GUI component text is formed into a localization pack file. The source language GUI component text of the localization pack file is translated to the target language. In response to the software application executing again, the translated GUI component text is loaded from the translated localization pack file. The GUI component is displayed with the translated GUI component text.