It makes sense for Portugal to have a sizable amount of Spanish speakers.
Per the immigration statistics by the statistics bureau, as of 2011 Portugal should have at very least 10,500. It would be great to add either this absolute number or the corresponding percentage (0.10 %) in the data.
Better data should be available later at http://ec.europa.eu/eurostat/statistics-explained/index.php/Foreign_language_skills_statistics (I also let the authors know).
Very small population mentioned, and it's not clear that it really needs to be added, or is very significant. E.g., the citation of 10,000+ is much smaller than the English-speaking population of Portugal, according to https://en.wikipedia.org/wiki/List_of_countries_by_English-speaking_population
Before adding this, it would be useful to find a statistical source that I can read (or have translated). And to know how useful it would really be, for CLDR purposes, to add this.
The usefulness for us as CLDR data users is that any non-zero value gives priority to the language. https://www.mediawiki.org/wiki/ULS/FAQ#language-territory
For the average user, the switch from Spanish to Portuguese and vice versa is more likely to be useful than the switch from Portuguese to English, because the two languages are more similar. We were asked by users to add this piece of statistic in order to help the sizable population of Spanish immigrants in Portugal. There are other numbers about said population (which changed a lot after the 2008 crisis) but I picked the safest source (the only official one available I could find) after hours of research. http://ec.europa.eu/eurostat/statistics-explained/index.php/Foreign_language_skills_statistics was filled in the meanwhile, but has no information on Spanish.
Do you want me to translate the relevant passages from the report I linked, or something else? Some time ago I added that same information to https://en.wikipedia.org/wiki/Immigration_to_Portugal#Immigration (column for 2011). Some other populations are bigger as of 2011, but are much more fluctuating.
As for English speakers, Eurostat provides per-country numbers of students studying each of the 3 most commonly studied languages. If Portugal has no number for English, that's an acceptable source. I can file that part separately now, but I think is more prioritary.
Thanks for this added explanation. Added it, with pop as 10,500.
The followup with Eurostat data is at