Apachean peoples speak one or more of seven Southern Athabascan languages, which have relatively similar grammatical structures and sound systems. Southern Athabascan (or Apachean) is a sub-family of the larger Athabascan family, which is a branch of the Nadene language family.

Navajo is notable for being the indigenous language of the United States with the largest number of native speakers. However, all Apachean languages are endangered, including Navajo. Lipan is reported extinct.
The Southern Athabascan branch was defined by Harry Hoijer primarily according to its merger of stem-initial consonants of the Proto-Athabascan series *k̯ and *c into *c (in addition to the widespread merger of *č and *čʷ into *č also found in many Northern Athabascan languages).
Hoijer (1938) divided the Apachean sub-family into an Eastern branch consisting of Jicarilla, Lipan, and Plains Apache and a Western branch consisting of Navajo, Western Apache (San Carlos), Chiricahua, and Mescalero based on the merger of Proto-Apachean *t and *k to k in the Eastern branch. When the Western languages have noun or verb stems that start with t, the related forms in the Eastern languages will start with a k.
He later revised his proposal in 1971 when he found that Plains Apache did not participate in the *k̯/*c merger to consider Plains Apache as a language equidistant from the other languages, now called Southwestern Apachean. Thus, some stems that originally started with *k̯ in Proto-Athabascan start with ch in Plains Apache while the other languages start with ts.
Apachean languages are tonal languages. Regarding tonal development, all Apachean languages are low-marked languages, which means that stems with a “constricted” syllable rime in the proto-language developed low tone while all other rimes developed high tone. Other Northern Athabascan languages are high-marked languages in which the tonal development is the reverse.
Southern Athabaskan languages
I. Plains      A. Kiowa–Apache (also called Plains Apache)
II. Southwestern
     A. Western

1. Chiricahua-Mescalero

a. Chiricahua

i. Chiricahua proper
ii. Warm Springs

b. Mescalero

2. Navajo (Navahu˙)
3. Western Apache (AKA Coyotero Apache)

a. Tonto (Northern Tonto, Southern Tonto)
b. White Mountain
c. San Carlos
d. Cibecue (ˀa˙paču)

     B. Eastern

1. Jicarilla (Apaches De La Xicarilla)
2. Lipan

Apache (Ndéé)
Apache is an Athabaskan (Na-Dene) language spoken by about 15,000 in mostly Arizona and New Mexico, with a few speakers in Texas. There are in fact two Apache languages: Western Apache and Eastern Apache, each of which has a number of dialects, including Jicarilla, Lipan, Kiowa-Apache, Chiricahua, and Mescalero. The Apache and Navajo languages are closely related.There are at least two distinct Apache languages: Western Apache and Eastern Apache. The two are closely related, like French and Spanish, but speakers of one language cannot understand the other well–in fact, Western Apache is closer to Navajo than to Eastern Apache. Chiricahua-Mescalero is considered by some people to be a dialect of Western Apache, by others a separate language; the three forms of Eastern Apache (Jicarilla, Lipan, and Plains Apache) are considered by some to be distinct languages and by others to be dialects of a single Eastern Apache language.
The name Apache probably comes from the Yuma word for “fighting-men” and/or from apachu, which means “enemy” in Zuni. This was what the Zuni called the Navajo, who in turn were called Apaches de Nabaju by the early Spanish explorers in New Mexico. They call themselves N’de, Inde or Tinde, which all mean “the people”.
Apache pronunciation

Sample text in Apache
‘Iłk’id́ą, k ǫǫ yá’édįná’a. ‘Ákoo Tł’ízhe hooghéí dá’áíná bikǫ’ ‘óliná’a. ‘Ákoo Tł’ízheí gotál yiis’́ąná’a. ‘Ákoo Mai’áee híłghoná’a. Gotál jiis’́ąí ‘áee, Mai tsíbąąee naaná’azhishná’a. ‘Ákoo bitseeí tsínáiłgoná’a.
Long ago, there was no fire. Then only those who are called Flies had fire. Then the Flies held a ceremony. And Coyote came there. At that place where they held the ceremony, Coyote danced around and around at the edge of the fire. And he continually poked his tail in the fire.
From: Coyote Obtains Fire, by Lawrence Mithlo
Famous Apache
Further Reading:
Western Apache-English Dictionary: A Community-Generated Bilingual Dictionary compiled by the White Mountain Apache TribeDictionary of Jicarilla Apache: Abáachi Mizaa Ilkee’ Siijai (Apache Languages and English Edition) Apache Jicarilla – This basic course in Jicarilla Apache provides vocabulary and sentence structures used in everyday Apache conversation. Following a pronunciation section, lesson units include dialogs, textual and grammar explanations, and exercises for review and practice.   A special feature is the regular comparison throughout the text of Jicarilla Apache with western Apache and other Apachean languages.A Practical Grammar of the San Carlos Apache Language – San Carlos Apache is a variety of Western Apache, a Southern Athabascan (or Apachean) language spoken on and around the San Carlos Reservation in east central Arizona, USA. The book ends with full Apache-English and English-Apache glossaries.

Navajo language

March 11, 2014

Navajo (Diné bizaad), pronounced Navaho, is an Athabaskan language of Na-Dené stock spoken in the southwestern United States. It is geographically and linguistically one of the Southern Athabaskan languages although the majority of Athabaskan languages are spoken in northwest Canada and Alaska. Navajo has more speakers than any other Native American language north of the […]

Apachean Languages
April 22, 2002

DULCE – Wilhelmina Phone, 72, stores an ancient treasure in her memory: a language known only to a dwindling handful of Jicarilla Apaches. Once each month, she and two other fluent Jicarilla speakers meet in Dulce with University of New Mexico linguists to develop the first-ever Jicarilla dictionary.

Apachean Languages