Both Spanish and Guarani are official languages. Most people in Paraguay speak Spanish and there is very limited use of English. Outside Asunción and the major cities, you will only hear Guarani. Because of the extensive use of Guarani, even those who have managed to learn Spanish do not always speak it very well.
In Paraguay, Guarani is almost always spoken as a mixture of Guarani and Spanish, known as Jopara, which means “mixed” in Guarani. The Guarani numerical system is rarely used and is almost always replaced by the Spanish numerical system.
In Paraguay, we use “vos” instead of “tu”. There is a small change in the conjugation, but not so big that you will not be understood if you use tu. This vos is NOT the same as vosotros. The verb stem does not change when you use vos, and the ending is always stressed. For example, “tienes” becomes “tenés”, “puedes” becomes “podés”, “vienes” becomes “venís”, etc.
In the northern and eastern parts of Paraguay, Portuguese is widely spoken. In some places, Nueva Esperanza (80% Portuguese speakers), Katuetè (60%), the majority speaks Portuguese, almost always the result of Paraguayans born in Paraguay or first generation Brazilian immigrants. There are many cases of Paraguayans born during the period of Brazilian immigration who speak only Portuguese at home, although they are also fluent in Guarani, but speak very little or no Spanish.
There are also a number of Mennonite communities in Paraguay that speak ordinary Low German and High German.