As part of today's Pixel 4a festivities, Google has snuck in a few other announcements as well. On top of the expansion of Live Caption, the snazzy new Assistant that debuted with the Pixel 4 is getting support for four more languages — eventually. German, French, Spanish, and Italian will all be getting the faster on-device version "soon."
The change was announced at two venues, in both Google's low-key Pixel 4a announcement blog post, as well as the Pixel 4 Google Assistant support page, which was updated to mention the additions in the last few days. Both say that support for the four new languages is coming, though a precise timeline for their addition isn't provided. While Google sometimes takes longer than expected to roll out changes these days, I'd expect the company wouldn't make the announcement a part of the support documents if it didn't actually mean "soon."
This follows the new Assistant's update earlier this year to support Japanese. Except English, none of the languages support continued conversation, so you'll have to keep triggering Assistant for each command.
In case you aren't familiar, the Pixel 4 (and now 4a) have a souped-up version of the Google Assistant with a slightly different UI, that works much more quickly by doing more processing on-device. Though it launched with some derpy limitations like mandatory gesture navigation and incompatibility with G Suite accounts, issues like those have since resolved, and device support is expanding. UI elements from the new version have also been spotted rolling out to devices with the older version of the Assistant.