The official language of Colombia is Spanish. Some indigenous tribes in rural areas continue to speak their own language, but almost all people from these tribes will be bilingual in their own language and in Spanish.
If you have recently learned Spanish, you will be relieved to know that the Bogotá dialect is clear and easy to understand. However, Spanish varies from Cartagena to Bogotá and Cali. In general, Spanish is spoken more quickly on the coasts, and Medellín Spanish has its own peculiarities. Note that in cities like Medellín and Cali, the dialect of Spanish is the voseo form. This means that instead of the familiar second person pronoun tú, vos is used. Although tú is also understood by everyone, vos is a friendlier form of address, while tú is reserved for intimate circles. The Spanish spoken on the Caribbean coast is similar to the dialects spoken in Cuba, Puerto Rico and the Dominican Republic.
Many Colombians know at least a few basic phrases in English, as English is taught in school and Hollywood films are usually in English with Spanish subtitles. In most cases, however, you should definitely invest in learning the basics of Spanish, as you will encounter many situations where no one will speak English.
Colombians from more affluent backgrounds are more likely to have learned English, and the majority of senior professionals, managers and government employees in Colombia speak an acceptable level of English.