I’m guessing Google don’t officially support Google Assistant with audio video devices in Portugal, which is why manufacturers, including but not limited to Sonos, don’t support it yet.

Out of curiosity I looked up countries Sony support for GA as I own one of their TVs. The list of supported countries and languages appears to be the same as Sonos at a glance, with Portugal, Portuguese listed as “not yet available”

https://www.sony.co.uk/electronics/support/articles/00201368

Google have a page of supported countries by product for their Store and again their home audio video products is limited and excludes Portugal.

https://support.google.com/store/answer/2462844?hl=en

GA for Android Auto, supports significantly more countries than any other product listed and appears to be the only product with an actual official list from Google. The majority of pages they have a non-committal availability may be limited by country and language.

https://partnermarketinghub.withgoogle.com/brands/android-auto/overview/country-availability/

Technically if Android Auto can support GA in so many countries any product could, but Google don’t appear to be making it available that way.

Realistically device manufacturers aren’t going to add GA to a product if Google don’t provide the integration as a supported service and just hope it works ok. 

What’s the address in your Sonos web profile? Did you try changing the country in that to a country where google assistant is available through Sonos? 

https://support.sonos.com/en-us/article/google-assistant-availability-on-sonos?language=en_US

I have Amazon Alexa working (in English) by having the Sonos address and Amazon address in US (I’m not there currently and Alexa isn’t here officially through Sonos). Could the same workaround work in PT for Google Assistant...

Amazon Alexa is available. 

I don’t want to use GA in pt_PT… en is my second language and I speak it perfectly. Also GA is available in Portugal, in en. So this should also work (in english)

Any way, yes, I am now “living” in Picadilly circus, London . still no avail. 

J​​​​​​​

Damn…. solved it… Phone was in pt_PT. 
Has to be in EN so to allow the activation of the GA as sonos App assumes that all around you is on that language.
You can then turn it back to pt.

Good that you found the solution and good to know about that. I have my devices use English so hadn’t noticed that requirement. I have some friends use non-English in their phones so now I’ll know what they should try.