My wife and I have very little knowledge of the Spanish language, but we have always felt comfortable driving anywhere in Costa Rica, getting gas, or even fixing a tire. Costa Ricans see a lot of tourists and they are exceptionally patient. Driving in Costa Rica requires no skill that any driver in the U.S. doesn't already possess. The most relevant pointer is that one must adjust driving time to account for 40-45 mph driving speeds.
Driving in Costa Rica is generally no big deal in most areas. However, there are some things to consider. First, it's impossible to treat most paved highways in Costa Rica as if one is driving on a U.S. highway. Most are two lanes with intermittent poor sections needing repair, and there are almost never shoulders on the roads. Passing cars is an art form. Even buses behave badly by U.S. standards. Travelers shouldn't start driving the way most Costa Ricans do (Costa Ricans will be the first to admit this). Play it safe and don't get in a hurry. One will likely be driving about 40 mph on most paved roads. Also, avoid San Jose if at all possible. The airport is actually outside of San Jose, so try and start with an itinerary that doesn't begin with the heaviest traffic going southeast from the airport.
Secondly, Officials are now asking for original passports if a driver is stopped for any infraction. Police used to accept a passport photocopy, but they are now looking for the real deal. There are a few checkpoints that are set up on roads just to check tourists. These are local uniformed police just doing their job. I don't worry much about them anymore, but one shouldn't go out driving without the original passport even on short day trips.
Thirdly, drivers should be very mindful of speed traps. Usually Costa Ricans are very good about flashing their lights and warning other drivers of upcoming speed traps. Pay attention to that. Drivers should not pay the police the cost of the ticket should a policeman ask- that's essentially a bribe. Nearly all minor traffic tickets can be paid at any national bank or even at some car rental agencies when the car is returned. No one is under any obligation to pay any policeman.
Fourth, road conditions are lousy at night. I generally don't drive when its dark unless it's a short hop to a restaurant.
Finally, one can hire a car the entire time in Costa Rica or just for specific birding trips... and rent the English speaking driver as well. Costa Rica Gateway offers such a service. This may cut down on the stress of driving while still allowing more freedom than a tour group. It can be particularly useful for destinations in the Central Valley when orbiting out of the San Jose Airport. However, it will be more costly. More general shuttle services in metro areas (that are not natural history oriented) can be found at Costa Rica Travel Transport and Liberia Costa Rica Transportation Online .
GOOGLE MAPS - Google Maps can be used from a Smartphone on some occasions. Like WAZE, one will have to turn "data roaming" on while in use. Google Maps is not quite the tool it should be in Costa Rica because what the driver actually sees on the ground is not always what is seen on a close-up, birds-eye view street map. Pay attention here: Streets are NOT marked with signage in Costa Rica and there are no street addresses. On a Google Map of San Jose, it might say turn right on Avenida 14, but a driver may never see a street sign for Avenida 14. One has to look for landmarks like a church or park or some other directional marker. The WAZE app seems to be a much better GPS system which effectively uses crowd-sourcing data to get you through odd traffic problems.
WAZE - If you have a smartphone, you will want to download the WAZE app. This app is regularly used in the United States, but it is now a regular traffic GPS system used in Costa Rica by the locals as well as tourists. The app is free, and the transition is seamless between its use in the U.S. and its use in Costa Rica. It is very easy to use, and it is absolutely essential when driving though urban environments in Costa Rican cities. It's a bit more visual than Google Maps with less reliance on street names.
You will have to turn on "data roaming" on your smartphone for the time you use it, but it's worth it. I turn "data roaming" off as soon as I stop using the app, but people use their phone in different ways when travelling. That's up to you.
One can rent a GPS system with a rental car, but it may add $10-15 a day to the cost. That can be kind of expensive, but if one has to drive through San Jose or Cartago, it will pay for itself. I only recommend it if you don't have a smartphone and can't manage the WAZE app which works just as well if not better. Please read this information regarding the GPS rentals from the REAL Costa Rica web
Trip Insurance - Trip insurance can be done over the Internet. We do this every year in case we have a serious accident in the car and have to be flown back. Collision insurance on the rental car won't cover that. Trip insurance will also cover theft on some items, and it will cover the expenses if the flight is cancelled or over 6 hours late - a growing problem for travelers. Most trip insurance will also eliminate the need for supplemental insurance when the car is rented - a handy advantage that gives it real value. One can get trip insurance online, and it won't take 15 minutes.
Maps - If one is a Facebook user, I strongly recommend visiting Costa Rica Guides\ Toucan Maps on Facebook. One can ask specific questions on driving issues, road conditions, distances, and general information on accommodations, food, and things to do. Toucan Maps also have one of the better hard copy maps of Costa Rica which is updated frequently. A few other good hard copy maps are available, but do some comparison before hand. One can order a Toucan map directly from their website.