An official language is a language that is given a special legal status in a particular country, state, or other jurisdiction. Typically a country's official language refers to the language used within government (e.g., courts, parliament, administration). Since "the means of expression of a people cannot be changed by any law",  the term "official language" does not typically refer to the language used by a people or country, but by its government.
Worldwide, 178 countries have at least one official language, and 101 of these countries recognise more than one language. Many of the world's constitutions mention one or more official or national languages.   Some countries use the official language designation to empower indigenous groups by giving them access to the government in their native languages. In countries that do not formally designate an official language, a de facto national language usually evolves. English is the most common official language, with recognized status in 51 countries. Arabic, French, and Spanish are also widely recognized.
An official language that is also an indigenous language is called endoglossic , one that is not indigenous is exoglossic .  An instance is Nigeria which has three endoglossic official languages. By this the country aims to protect the indigenous languages although at the same time recognising the English language as its lingua franca.
Around 500 BC, when Darius the Great annexed Mesopotamia to the Persian Empire, he chose a form of the Aramaic language (the so-called Official Aramaic or Imperial Aramaic) as the vehicle for written communication between the different regions of the vast empire with its different peoples and languages. Aramaic script was widely employed from Egypt in the southwest to Bactria and Sogdiana in the northeast. Texts were dictated in the native dialects and written down in Aramaic, and then read out again in the native language at the places they were received. 
The First Emperor of Qin standardized the written language of China after unifying the country in 221 BC. Classical Chinese would remain the standard written language for the next 2000 years. Standardization of the spoken language received less political attention, and Mandarin developed on an ad hoc basis from the dialects of the various imperial capitals until being officially standardized in the early twentieth century.
According to an undated chart by the American pro-English-only organization known as U.S. English, 178 countries have an official language at the national level. Among those, English is the most common with 67 nations giving it official status. French is second with 29 countries, Arabic is third with 26 countries and Spanish is fourth with 19 countries, Portuguese is the official language of 9 countries and German is official in 6. Some countries—like Australia, United Kingdom and the United States —have no official language recognized as such at national level. On the other extreme, Bolivia officially recognizes 37 languages, the most by any country in the world. Second to Bolivia is India with 23 official languages.
The selection of an official language (or no official language) is often contentious.  An alternative to having a single official language is "official multilingualism ", where a government recognizes multiple official languages. Under this system, all government services are available in all official languages. Each citizen may choose their preferred language when conducting business. Most countries are multilingual  and many are officially multilingual. Canada, Philippines, Belgium, Switzerland, and the European Union are examples of official multilingualism. This has been described as controversial and, in some other areas where it has been proposed, the idea has been rejected.  It has also been described as necessary for the recognition of different groups  or as an advantage for the country in presenting itself to outsiders. 
In specific countries
In accordance with the Constitution Act, 1982 the (federal) Government of Canada gives equal status to English and French as official languages. The Province of New Brunswick is also officially bilingual, as is the Yukon. Nunavut has four official languages. The Northwest Territories has eleven official languages. All provinces, however, offer some necessary services in both English and French.
Canadian advocates of a single official language say it promotes national identity.  In Canada, debate has focused on whether the local majority language should be made the exclusive language of public business. In the Canadian province of Quebec, for example, laws restrict the use of the minority English in education, on signs, and in the workplace. 
German is the official language of Germany. However, its minority languages include Sorbian ( Upper Sorbian and Lower Sorbian), Romani, Danish and North Frisian, which are officially recognised. Migrant languages like Turkish, Russian and Spanish are widespread, but are not recognised official languages.
Hong Kong has two official languages: English and Chinese. Hong Kong Cantonese is used in daily conversation and Traditional Chinese used to be the only writing system in Hong Kong before the 1997 handover. However, in Mainland China the official language is Mandarin and Simplified Chinese is used as the standard writing system. As time goes by, some of the signage in Hong Kong has been converted to Simplified Chinese characters due to its popularity in China and around the world. Also, as more and more people from the mainland visit Hong Kong, Traditional Chinese characters seem to be disappearing due to the impracticality of having two sets of Chinese characters. Some companies may have changed the characters of the signs whilst nearly all Hong Kong people continue to use traditional characters. 
The Eighth Schedule of the Indian Constitution lists 22 languages,  which have been referred to as scheduled languages and given recognition, status and official encouragement. In addition, the Government of India has awarded the distinction of classical language to Tamil, Sanskrit, Kannada, Telugu, Malayalam and Odia.
Hebrew and Arabic are the official languages of Israel. In most public schools, the main teaching language is Hebrew, English is taught as a second language, and most students learn a third language, usually Arabic but not necessarily. Other public schools have Arabic as their main teaching language, and they teach Hebrew as a second language and English as a third one. There are also bilingual schools which aim to teach in both Hebrew and Arabic equally.
Some languages other than Hebrew and Arabic, such as English, Russian, Amharic, Yiddish and Ladino enjoy a somewhat special status, but are not considered to be official languages. For instance, at least 5% of the broadcasting time of privately owned TV-channels must be translated into Russian (a similar privilege is granted to Arabic), warnings must be translated to several languages, signs are mostly trilingual (Hebrew, Arabic and English), and the government supports Yiddish and Ladino culture (alongside Hebrew culture and Arabic culture).
The Constitution of Latvia (or Satversme) designated Latvian as the state language. In 2012 there was initiative to hold a referendum on constitutional amendments, elevating Russian as a state language. Kristīne Jarinovska in her analysis describes the proposal in the following way:
It proposed several constitutional amendments for introducing Russian as Latvia's second official language—i.e., amendments to the Satversme’s Articles 4 (on Latvian as the state language), 18 (on the solemn promise of a member of Parliament to strengthen the Latvian language), 21 (on Latvian as the working language of the Parliament), 101 (on Latvian as the working language of local governments), and 104 (on the right to receive a reply to a petition in Latvian). Obviously, the proposed amendments would have influenced other constitutional norms as well. Moreover, since Article 4 of the Satversme alike norms of independence, democracy, sovereignty, territorial wholeness, and basic principles of elections that form the core of the Satversme (according to Article 77 of the Satversme), the initiative, in fact, proposed discontinuing an existing state and establishing a new one that is no longer a nation-state wherein Latvians exercise their rights to self-determination, enjoying and maintaining their cultural uniqueness 
New Zealand has three official languages.  Official status can be used to give a language (often indigenous) a legal status even if that language is not widely spoken, and in New Zealand, the Māori language and New Zealand Sign Language both have de jure official status under the Māori Language Act 1987 and New Zealand Sign Language Act 2006  respectively, even though less than five percent of New Zealanders speak te Reo Māori.  New Zealand provides information about enrolling and voting in 27 languages. 
Urdu is the national language of Pakistan. Urdu and English both are official languages in Pakistan.
Russian is the official language of the Russian Federation and in all federal subjects, however many minority languages have official status in the areas where they are indigenous. One type of federal subject in Russia, republics, are allowed to adopt additional official languages alongside Russian in their own constitutions. Republics are often based around particular native ethnic groups, and are often areas where ethnic Russians and native Russian-language speakers are a minority.
South Africa has eleven official languages that are mostly indigenous. Due to limited funding, however, the government rarely produces documents in most of the languages. Accusations of mismanagement and corruption have been leveled against the Pan South African Language Board, which is in charge of maintaining the system.
At the federal level, the United States has no official language, but 32 of the 50 U.S. states  and all six inhabited U.S. territories have designated English as one, or the only, official language, while courts have found that residents in the 50 states do not have a right to government services in their preferred language.  Public debate in the last few decades has focused on whether Spanish should be recognized by the government, or whether all business should be done in English. 
At the state level, California allows people to take their driving test in the following 32 languages: Amharic, Arabic, Armenian, Chinese, Croatian, English, French, German, Greek, Hebrew, Hindi, Hmong, Hungarian, Indonesian, Italian, Japanese, Khmer, Korean, Laotian, Persian, Polish, Portuguese, Punjabi, Romanian, Russian, Samoan, Spanish, Tagalog/Filipino, Thai, Tongan, Turkish, and Vietnamese. 
New York state provides voter-registration forms in the following five languages: Bengali, Chinese, English, Korean and Spanish. The same languages are also on ballot papers in certain parts of the state (namely, New York City). 
The pro-English-only website U.S. English sees a multilingual government as one in which its "services actually encourage the growth of linguistic enclaves...[and] contributes to racial and ethnic conflicts".  Opponents of an official language policy in the United States argue that it would hamper "the government's ability to reach out, communicate, and warn people in the event of a natural or man-made disaster such as a hurricane, pandemic, or...another terrorist attack".  Professor of politics Alan Patten argues that disengagement (officially ignoring the issue) works well in religious issues but that it is not possible with language issues because it must offer public services in some language. Even if it makes a conscious effort not to establish an official language, a de facto official language, or the " national language ", will nevertheless emerge.  Indeed, two-thirds of Americans believe that English is the United States' official language. 
Sometimes an official language definition can be motivated more by national identity than by linguistic concerns. When Yugoslavia dissolved in 1991, the country had four official languages— Serbo-Croatian, Slovene, Albanian and Macedonian. Serbo-Croatian was used as a lingua franca for mutual understanding and was also the language of the military.
When Croatia declared independence (1991) it defined its official language as Croatian, and Serbia likewise defined its official language as Serbian. Bosnia-Herzegovina defined three official languages: Bosnian, Croatian, and Serbian. The different "languages" are mutually intelligible and linguists see them more as dialects of Serbo-Croat rather than as distinct languages. Critics allege that the Bosnian government chose to define three languages to reinforce ethnic differences and keep the country divided.  The language used in Montenegro, traditionally considered a dialect of Serbian, became standardized as the Montenegrin language upon Montenegro's declaration (2006) of independence.