They've since implemented a solution using what they call "location extension fields", where you will get extra checkout fields depending on your store's location.
I know Brazil is one of them, but I'm unsure about Portugal.
I was checking the Shopify Changelog and it seens that this was also extended to Italy, but still isn´t available in Portugal. I really don´t understand why this is not extended to other European countries.
Hi @lucaspon thanks for pointing this out. I knew about the Brazil one but not about others, if they are adding more countries it seems likely that they will also add Portugal sooner or later... It is just such basic yet important feature that I don't understand why it has to taken so long, or even why it has to happen on a 'per country' basis.