Avoidance speech

Avoidance speech is a group of sociolinguistic phenomena in which a special restricted speech style must be used in the presence of or in reference to certain relatives. Avoidance speech is found in many Australian Aboriginal languages and Austronesian languages as well as some North American languages, Highland East Cushitic languages and Bantu languages. Chinese naming taboo prohibits speaking and writing syllables or characters that appear in the names of esteemed people, such as emperors, parents, and ancestors. 
Avoidance speech styles tend to have the same phonology and grammar as the standard language they are a part of. The lexicon, however, tends to be smaller than in normal speech since the styles are only used for limited communication.
Australia.
Avoidance speech in Australian Aboriginal languages is closely tied to elaborate tribal kinship systems in which certain relatives are considered taboo. Avoidance relations differ from tribe to tribe in terms of strictness and to whom they apply. Typically, there is an avoidance relationship between a man and his mother-in-law, usually between a woman and her father-in-law, and sometimes between any person and their same-sex parent-in-law. For some tribes, avoidance relationships are extended to other family members, such as the mother-in-law's brother in Warlpiri or cross-cousins in Dyirbal. All relations are classificatory – more people may fall into the "mother-in-law" category than just a man's wife's mother.
Avoidance speech styles used with taboo relatives are often called mother-in-law languages, although they are not actually separate languages but separate lexical sets with the same grammar and phonology. Typically, the taboo lexical set has a one-to-many correspondence with the everyday set. For example, in Dyirbal the avoidance style has one word, "jijan", for all lizards, while the everyday style differentiates many varieties. In Guugu Yimidhirr the avoidance speech verb "bali-l" "travel" covers several everyday verbs meaning "go", "walk", "crawl", "paddle", "float, sail, drift", and "limp along". Corresponding avoidance and everyday words are generally not linguistically related. Avoidance forms tend to be longer than everyday forms.
In some areas, the avoidance style is used by both members of the avoidance relationship; in others the senior member may talk to the junior in everyday style. Behavior associated with avoidance speech is a continuum and varies between tribes. For the Dyirbal people, a man and his mother-in-law may not make eye contact, face one another or directly talk to each other. Rather, they must address a third person or even a nearby object. For slightly less restricted relationships, such as between a man and his father-in-law, avoidance style is used and must be spoken in a slow, soft voice. An extreme case of avoidance behavior is found in the Umpila, in which a man and his mother-in-law may not speak at all in each other’s presence.
Children in these cultures acquire avoidance speech forms as part of their normal language development, learning with whom to use them at a fairly young age. Additionally, a few languages have another style, called a "secret language" or "mystic language", that is taught to boys as part of initiation rituals, and is only used between men.
There is also the tradition of, during the mourning period, avoiding reference to the names of people who have died as a mark of respect—and also because it is considered too painful for the grieving family. Today the practice continues in many communities, but has also come to encompass avoiding the publication or dissemination of photography or film footage of the deceased as well. Most forms of media in Australia include a disclaimer warning Aboriginal and Torres Strait Islanders that the material may contain images and voices of such people who have died. This is recommended by the Australian Broadcasting Corporation.
The avoidance period may last anywhere from 12 months to several years. The person can still be referred to in a roundabout way, such as, "that old lady", or by their generic skin name, but not by first name. In some Central Australian communities, if for example, an individual named Alice dies, that name must be avoided in all contexts. This can even include the township Alice Springs being referred to in conversation in a roundabout way (which is usually fine, as the Indigenous name can be defaulted to). Those of the same name as the deceased are referred to by a substitute name during the avoidance period such as "Kuminjay", used in the Pintubi-Luritja dialect, or "Galyardu", which appears in a mid-western Australia Wajarri dictionary for this purpose.
Africa.
A special system of avoidance vocabulary is traditionally used by married women speaking Highland East Cushitic languages in southwestern Ethiopia. In Kambaata and Sidamo, this system is called "ballishsha", and includes physical and linguistic avoidance of parents-in-law. Women who practice "ballishsha" do not pronounce any words beginning with the same syllable as the name of their husband’s mother or father. Instead, they may use paraphrase, synonyms or semantically similar words, antonyms, or borrowings from other languages.
"Hlonipha", or "isihlonipho", is a traditional system of avoidance speech in Nguni Bantu languages of southern Africa including Zulu, Xhosa and Swazi, as well as Sotho. This special speech style and correlating respectful behaviors may be used in many contexts, but is most strongly associated with married women in respect to their father-in-law and other senior male relatives. Women who practice "hlonipha" may not say the names of these men or any words with the same root as their names. They avoid the taboo words phonologically (substituting sounds) or lexically (substituting words with synonyms, etc.). The "hlonipha" system also includes avoidance of the names of certain relatives by all speakers and physical avoidance of certain relatives.