As in the case of many other communities living in Berlin, it is very difficult to estimate how many Portuguese and Brazilians live in the German capital city. But I've met a couple of them in the last four years and I saw several good shops with traditional food and even a couple of restaurants.
The final element that I was missing was the bookstore and I finally was in time with my working schedule to pay a visit to ALivraria. It is a relatively small space, situated 10 minutes by foot from Rosenthaler Platz. When I visited the store it was around 2pm and except a lady who say 'hello' and asked me in Portuguese if I need something, was no one around.
The most part of the space is taken by books. I was excepting a second hand bookstore, with many used books, but I found instead several good translations, mostly novels, but also cooking and history books, both in Portuguese and Brazilian Portuguese. The prices are expensier than in a normal bookstore, but probably this is because of the taxes and transportation expenses.
Unfortunatelly, you do not have too much space to stay and read 10-12 pages, but probably if you want a chair to spend more time, you can ask and you will have it.
In the second room you can find some local food specialities, with many beers and drinks, but also some corn-based products. Did not check the prizes but I suppose it is that kind of food that you will want to afford once when you are ready to cook a thematic cooking evening.
In addition, you can have various information about events in Portuguese, classes - for singing or learning German. I was told that some dating tips are also offered for the single boys and girls in love with Portuguese language, but I did not find anything like this when I visited the place. I am thinking about returning soon there for getting some Portuguese books to improve my language - included on my to-do-list for over 2 years without tremendous results.