Is it better to take buses or planes?

Buses are better for the budget and the experience, but only for trips under 12 hours. Anything longer, and the cost of food and potential safety issues make a $100 budget flight a better value.

Do I need to speak Spanish?

You don't need to be fluent, but learning 50 basic phrases is non-negotiable for finding bus terminals, ordering food, and handling emergencies.

How to plan a backpacking route through South America

Prioritize two or three neighboring countries rather than trying to see the whole continent in one trip. Focus on one geographic corridor, like the Andes or the Atlantic coast, to minimize time spent on long-haul buses and maximize your time exploring.

Pick a single corridor. South America is massive. Stick to either the 'Gringo Trail' (Peru, Bolivia, Ecuador) for high-altitude culture, or the Southern Cone (Argentina, Chile) for Patagonia and wine regions. Mixing both requires expensive domestic flights.
Identify your 'must-sees' and 'skip-its'. List your top three experiences (e.g., Machu Picchu, Salar de Uyuni, Torres del Paine). Map them and discard anything more than 24 hours of bus travel away from that cluster. If it doesn't fit the flow, save it for a second trip.
Use buses for short hauls, flights for long jumps. Budget $30-$50 for 8-12 hour bus rides. Anything over 18 hours is exhausting; look for low-cost carriers like JetSmart or Sky Airline to jump those distances for $80-$120 if booked 3 weeks out.
Account for elevation changes. If moving from sea level to the Andes, schedule two 'acclimatization days' in your itinerary where you do absolutely nothing but drink water and walk slowly. Do not schedule a hike or tour for your first 48 hours in Cusco or La Paz.

Is it better to take buses or planes?: Buses are better for the budget and the experience, but only for trips under 12 hours. Anything longer, and the cost of food and potential safety issues make a $100 budget flight a better value.
Do I need to speak Spanish?: You don't need to be fluent, but learning 50 basic phrases is non-negotiable for finding bus terminals, ordering food, and handling emergencies.