This one thoroughly impressed me. You can now ask Siri to translate anything in 10 languages, no internet or iPhone connection needed. To test this, I toggled Airplane Mode on my Watch, made sure it had no iPhone connection, then asked Siri “how do I say ‘how are you’ in Chinese?” Pretty cool.
Supported languages as of this writing are Arabic, Chinese, English, French, German, Italian, Japanese, Korean, Portuguese, Russian, and Spanish.