If you're a foreigner and you don't know how to speak Spanish, it would be a shame for you to miss out on Costa Rican sayings and language in general. Even though a lot of people living in the capital city of San Jose speak some English, (especially those people in the tourist trade), you won't encounter many English-speakers in more rural areas. It's always advisable to learn at least the basics, so that your stay can be more enjoyable and less stressful.
Costa Ricans don't use the same Castilian Spanish that's spoken in Spain. The Spaniards lisp their c's and z's and they use the "vosotros" person, while Costa Ricans use the antiquated form of "vos", and the more formal "usted". They all mean "you" but they vary in their formality and they affect verb conjugations. Costa Rican Spanish is as dynamic a language as any other, and it's full of "Tiquismos" or unique sayings and argot. One of the common Tiquismos is the use of the diminutive Costa Ricans are called "ticos" because they add this word as a suffix in order to create a diminutive.
In other words, instead of saying "blanquito" (small, white), they might say "blanquitico" or "blanquititico", which means the same thing. Ticos also use tons of terms of endearment, which shouldn't be misinterpreted as mean nicknames. For instance, it's common for Ticos to call people "flaco" (thin one) or "gordo" (fat one) without intending any offense at all. People of other races are usually called by their race, as in "chino" (chinese) or "negro" (black one). Apart from the unique "Tiquismos", Costa Rican Spanish isn't really that difficult to learn. Ticos speak more slowly and clearly than in other Latin American countries. Ticos are also extremely patient with people who are trying to learn their language, and they will help and encourage them to do so. It's advisable to learn at least the basics of the language, since as was mentioned before, only some people speak English. The only large population of native English speakers is located in Limon, where people of Jamaican descent settled.
Costa Rican Spanish, as most Spanish in Latin America, is extremely polite and sometimes formal. Some key words to learn, in order to keep up with the politeness are: "Gracias" (thank you), "Por favor" (please), "Buenos dias" (good morning). Ticos also mention luck and God a lot in their speech: "Que Dios lo acompane" (May God go with you), or if you meet them for the first time "Mucho gusto" (It's a pleasure).
Language schools abound in Costa Rica, and they range from a few mediocre ones to a majority of excellent ones. There are even language schools in rural areas, near rainforests or in beach areas, that offer a good combination of exotic living and language learning for the more adventure-type travelers.
All in all, Costa Rica is an excellent option for learning Spanish in an easy and gradual way. There are intensive 2-4 week courses and semester and yearly programs for the more ambitious types.