English is widely spoken in Portugal, especially in the larger cities and in the Algarve. Plenty of foreigners live comfortably and reasonably efficiently speaking only in English. (In fact, it can be difficult to find a Portuguese who will speak to you in Portuguese.)
Most websites and apps (banking, for instance) have English versions, and there’s usually a “press 2 for English” option when calling official phone numbers, such as for the immigration office or the national health service 24-hour hotline. For in-person bureaucratic matters, it’s generally allowed to being a friend who can translate, or in some cases, they’ll provide an interpreter (on the rare occasion that the person you speak with isn’t themselves fluent in English).
Bilingual menus are available in most Portuguese restaurants
In daily life, almost everyone speaks enough English to say “let me get my colleague”—and then finds that English-speaking colleague. Oftentimes, another customer will step in and help with translation.
In most cases, most Portuguese genuinely like to help. They also like to speak English, particularly those under age 50 or so. English is taught in schools from an early age, and it’s the common language in much of higher education. Many of these graduates will got to work in tourism or globally-minded companies. You’ll also find that some of the population learned English from watching TV. English-language films and series in Portugal aren’t dubbed, but are subtitled instead. (Ironically, and perhaps apocryphally, this is because during the time of the dictatorship, when much of the population was illiterate, not dubbing media was a way of limiting people’s contact with outside ideas.)
But just because you can live in Portugal and only speak English…doesn’t mean you should. It’s satisfying to be self-sufficient in a cafe or a grocery store, for instance, without asking anyone to get their colleague. It improves your social life. Most Portuguese appreciate it when you make an effort (even if they then switch back to English), and they’ll likely tell you that your accent is cute.
Of course, it’s also nice to know more about what’s happening around you. So, if you want to have more than a very basic idea of the local or national news, you’ll need to read or understand some Portuguese. And, it’s also just polite.
Oh, and whatever you do…don’t speak Spanish!