The language addition applies to all of Google's smart speakers -- the original Google Home, the Mini and the Google Home Max. You command Google's smart speakers with voice commands, so the extra language will make life much easier for Spanish speakers. The wake word is "OK, Google," same as in English.
Google brought its smart speakers to Spain last week, so the company is clearly making a push into the Spanish-speaking world. Those in Spain could talk to it in Spanish last week, but Google's just now bringing Spanish language capabilities to the left side of the pond.
In English or Spanish, you can now ask about your day, control your smart home, search the web and more. The Google Assistant that powers Google Home can also speak French, German, Italian and Japanese.