https://www.cnbc.com/2018/08/30/googles-assistant-home-smart-speaker-multiple-languages-bilingual-.html

No need to fiddle with with the settings: Google's smart assistant and Home speaker are now bilingual, allowing users to issue commands in two different languages interchangeably. Previously, users would have to manually switch back and forth between individual languages.

It's a thorny artificial intelligence problem that requires the Assistant to run multiple processes in parallel: It must identify which language a user is speaking while simultaneously parsing their command. (Learn more about how Google made it work here.) Although different smart assistants like Amazon's Alexa, Apple's Siri and Microsoft's Cortana can all be set up to understand and speak a wide range of different languages, Google is the first to support multiple languages at once.