how do I localise all the strings in my app

To localize all the strings in your app, you can utilize the tools and techniques discussed in the WWDC sessions "Build multilingual-ready apps" and "Meet the Translation API."

String Catalogs: In the session "Build multilingual-ready apps," it is highlighted that string catalogs are essential for managing translations in your project. They help keep strings in sync with your code and offer powerful editing tools. New features include detecting common validation issues and marking specific strings as "don't translate" to inform translators that content is still being finalized. This can greatly accelerate your localization workflow.
Translation API: The session "Meet the Translation API" discusses how to add translation features to your app. This is particularly useful for user-generated content that may not be covered by traditional localization. The API allows you to translate text dynamically, supporting multiple languages and providing options for batch translation.
Automatic Grammatical Agreement: The "Build multilingual-ready apps" session also introduces an automatic grammatical agreement engine, which helps personalize and make your app more inclusive by using terms of address and pronouns based on language and region settings.
Language and Region Settings: You can ensure that your app respects the user's language and region settings, which includes handling number formatting and allowing users to choose an app-specific language independently of the device language.

For more detailed guidance on implementing these features, you can refer to the specific sessions:

Build multilingual-ready apps (Localization)
Meet the Translation API (Flexible translation)

These sessions provide comprehensive insights into making your app multilingual-ready and enhancing the user experience across different languages.