I do not always let people know I speak spanish as you will quickly be asked to undertake all kinds of things. I often have people on the phone saying “can you speak to this person for me” or asked to call for them including, ordering logs for the fire, dealing with Telefonica. It can turn into a nightmare. Once had someone call me and ask to speak to a Policeman who had arrived with a denuncia. Another time I was asked to translate in a dispute between neighbours, result was that they both took my words personally and neither of them was speaking to me.
I wouldn’t care to live in a country if I didn’t at least speak some of the language. I also find it strange that here on the CDS many Spanish people cannot speak English as most of the economy is based around Brit tourism.