Chewa, also known as Nyanja, is a Bantu language spoken by 12 million people in much of Southern, Southeast and East Africa, namely the countries of Malawi and Zimbabwe, where it is an official language and Mozambique and Zambia where it is a recognised minority language. The noun class prefix chi- is used for languages, so the language is usually called Chichewa and Chinyanja (spelled Cinianja in Mozambique). In Malawi, the name was officially changed from Chinyanja to Chichewa in 1968 at the insistence of President Hastings Kamuzu Banda (himself of the Chewa people), and this is still the name most commonly used in Malawi today. In Zambia, the language is generally known as Nyanja or Cinyanja/Chinyanja '(language) of the lake' (referring to Lake Malawi).

For more than 15 million people in Malawi, Tanzania, Zambia, Mozambique, Botswana, Zimbabwe and South Africa, Chinyanja or Chichewa has become the most important language of daily life.The language has gained importance and strength by developments in its written and oral use, and because an increasing number of its speakers have come to discover and emphasise their common linguistic heritage and practice. In that way it has become an intermediary language for all Malawians, and for many ethnic groups in the whole of Central and Southern Africa.

Although the official language in Malawi is English, the Chichewa language is spoken by more than 50% of the population. Apart from the two, other languages spoken in Malawi are Chinyanja Yao, Chiyao, Tonga, Chitumbuka, Nkhonde, Tumbuka, Lomwe, Lambya, Nyiha, Ndali, Kacchi, Kokola, Zulu, and Afrikaans.

Zambia is also considered a multilingual country but its government only recognizes one language as official: English. Of the 17 million people in Zambia, only 1.91 million can speak or understand English. Chichewa is a minority language, spoken by 2 million people and Bemba is the most prominent of the 70 languages spoken with about 3 million native speakers.

The people of Malawi are predominantly Christian with a minority Muslim population of about 13%. Zambia is also predominantly Christian.

Sources:
Wikipedia
https://www.graphicmaps.com/malawi/languages