Very interesting question. I think we will have loads of different scenarios and circumstances with UK nationals and this whole Brexit withdrawal residency in the next 10 years.
anywho, in the current SEF brexit portal there is some text in the FAQ that the new residence permit being issued out to UK residents under the withdrawal agreement is only temporary and will always be issued with a 5 year period. Apparently we can apply to reduce this ‘after’ receiving the card to include the years already spent in portugal as per the original CRUE. If anyone tries that please update about your experience here.
Usually after 5 years, the holder can apply for permanent residency and/or citizenship. But in your case it is 3 years however I think you will have to change to a card first. But then possibly have to request the change in date to reflect the time already spent since your CRUE.
I’m not sure about language requirement. Someone else can educate me on it.
hope that was helpful.