Many years ago I was in Teatro Avenida chatting with my companion waiting for the curtain to come up when the woman sitting next to me on the other side tapped me on the arm and, in perfect RP, asked me if I were English. We had a short conversation and just before the lights went down I asked her where she was from. I expected her to say Oxford, London, Weybridge or some such. Oh, I'm from here, Buenos Aires, came the reply. Such a shame that I didn't realise that earlier because I had assumed we were talking Englishman to Englishwoman and I missed the opportunity to chat with her as a local. I look on that as an example of the downside of speaking a foreign language perfectly.
I have always struggled with foreign languages yet seem cursed to have to speak them to the end of my days. I made an abject failure of French at school; struggled with German when I needed it for business; gave up Russian pretty quickly then, just when I thought I could get away from all that language stuff, I fell in love with an Argentine. Will it ever end, I ask? What's more, my hearing continues to get worse and ironically I comprehend foreigners (Brits, Germans, Dutch, Poles etc) when they speak Spanish better than native Spanish speakers of any origin.
I studied Spanish in the UK up to the Higher College Certificate (whatever that means) and one to one tuition in Argentina but I still don't think I'm any good so here are my rules for survival.
Only master spies who want to infiltrate a foreign government service need a perfect accent and I accept mine is far from perfect but some people find it endearing.
Of course it's helpful to know if people are swearing at you but there's a awful lot of language I would never use at home so why learn it here?
I use the subjunctive mood a lot. It's not very Argentine but it reflects the way I speak in English and I see that as a way my personality comes through. Besides, it means that I don't have to memorise quite so many Spanish irregular verbs!