Whilst the government is currently pushing English language education in schools (many universities require students to study English) you may have trouble finding people on the street who speak conversational English.
In more affluent and tourist friendly neighborhoods, such as El Poblado, there will usually be someone at the hostel, hotel, bar, or restaurant that speaks English. It’s also common for menus to have an English description or English version altogether.
The locals in suburbs such as El Poblado are more likely to speak English having had more opportunity to live, study and/or work abroad. Elsewhere, despite the language barrier the locals are friendly and will do their best to try and understand you. Body language goes along way.
All in all Colombia is a superb place to learn the Spanish language. Spanish is spoken relatively clearly, but more importantly, it’s much easier to learn the local language in such an affectionate and warm country. Even if your Spanish is terrible but you carry a smile, strangers exude patience and might even compliment your Spanish. This local Colombian morale boost, alone, will surely get you through a potential language barrier easier than in other Spanish speaking countries where they might be more reserved and unapproachable.
Of course if you want to learn Spanish in Medellin you are more than welcome to join us at the Toucan Spanish School. We’re the largest Spanish School in Medellin, classes start weekly at all levels.