The Luangwa Valley, largely covered by the Eastern Province of Zambia is, arguably, the least developed. Some say this is because it's simply the most inaccessible. However, the Luangwa Valley is notorious for failing to support former President Frederick Chiluba in either of his bids for office. Therefore, some interpret underdevelopment as a kind of punishment.
Nevertheless, Eastern Province retains one of Zambia's most precious resources — South Luangwa National Park. Possibly the best game park in Africa, South Luangwa boasts four of the Big Five (sorry, Zambia's only rhino are in Livingstone) coupled with extremely low tourist traffic (due, in large measure, to its inaccessibility). No other game park in Africa can match this combination.
Nyanja is the language most spoken in the Eastern Province, although Tumbuka, Chewa, Senga are also popular.
Actually, Nyanja is a variant of Chewa. The Chewa people in Eastern Zambia are referred to as "Nyanja" speaking because when they arrived in Eastern Zambia they commonly used the praise term "Ife a ku Nyanja", meaning "We people of the lake". Nyanja is a Chewa word for lake. Before the Chewa people settled in Eastern Zambia, they passed through modern day Malawi along the shores of lake Malawi. Their fascination with this big body of water made them continue to refer to it long after they had left it behind.
Chipata is roughly 12 km from the border of Malawi along Lusaka Road. Taxis taken from the Malawian side can take you to Malawi customs, but you'll have to change once on the Zambian side.