RsyncOSX and the menu app RsyncOSXsched are prepared for localization. Default language for both is English.

RsyncOSX is localized to:

Localization is done by utilizing Crowdin to translate the xliff files which are imported into Xcode after translating. Xcode then creates the required language strings. Crowdin is free for open source projects.

Volunteers are wanted for translating to other languages. Please create an issue if you have possibility to translate. Translating to new languages is mostly a proofreading exercise. Crowdin does most of the work and proofreading is last step before importing into code.