Apple Xliff (xliff, xlf)
Apple XLIFF is the exchange format generated by Xcode for exporting and importing localizations in bulk. XLIFF (XML Localization Interchange File Format) is an industry-standard XML format, and Xcode's variant bundles all translatable strings from an iOS, macOS, or visionOS project into a single file per locale — both Localizable.strings entries and interface builder string attributes from storyboards and XIBs.
Xcode XLIFF files contain trans-unit elements for every translatable string. Each unit has a source element with the original text, a target element for the translation, and a note element carrying the developer comment. The file-element reference attributes identify which storyboard or strings file each unit originates from, enabling Xcode to import translations back into the correct locations.
Best practice: add translator notes to every NSLocalizedString call before exporting — these appear in the note element and are the context translators rely on. Use Xcode's Product menu to export XLIFF files, translate via Language Monster, and import the completed files back. Define custom, stable identifiers for your i18n attributes in interface builder rather than relying on auto-generated identifiers — stable IDs make Translation Memory matching far more effective across Xcode versions.