English Around the World
English teachers generally would not identify any variety of speech as "authentic", because this word has specific moral and social significance outside the scope of learning a language. However, for educational purposes, each teacher or school generally will identify some dialect as a model for the rules and habits to teach students. In places with no significant population that speaks English, students usually learn following either a British or American standard. This choice usually depends on region or country.
A teacher or school will generally choose either a British or American standard, and in particular a Received Pronunciation (RP) or General American (GA) accent, because they are most familiar to English speakers across the world, and so learning one of them makes it easiest for a student to understand others, and to be understood by them.
Rarely does anyone speak completely as British or Americans unless native, and not all native to the United Kingdom or even to England speak RP, or to the United States speak GA. However, how well someone communicates with native speakers of England or the US may provide a useful test for how well that individual may communicate internationally in English, simply because others will likely use a similar standard. In this sense, many would consider the British and American dialects to be neutral standards, which create a balancing effect, on the worldwide use of the language. Some may further consider this influence to elevate British or American English to a position of privilege, but such specific characterization is generally not helpful, and often leads to inaccurate conclusions and harmful behaviors.
English in India
In India and the other countries of South Asia that follow from the influence of British rule, the combined count of individuals who speak English is almost as great as in the United States, and is more than twice as great as the combined count in the United Kingdom, Canada, and Australia.
Indian English is a distinct standard, which determines how students study English in India and nearby countries.
Outside of South Asia, however, students are unlikely to be instructed in speaking English as do Indians.
Indian Accents Around the World
Those who understand English generally, tend to understand Indian English. Certain features of Indian speech sometimes cause difficulties for non-Indians to understand Indians in English. The degree and effect of these features depends on the individual speaker. Sometimes, but not always, these differences diminish naturally for Indians after having moved overseas.
Many native speakers of English have limited experience listening to Indians, whereas a larger proportion of Indians may have regular exposure to British and American media. Such disparities sometimes cause surprises.
An individual accustomed to speaking English among other Indians, as well as to hearing English from both Indian and foreign sources, may feel confused or frustrated during first conversations with non-Indians, because of difficulty being understood.
Someone affected by or concerned with these differences may choose simply to modify habits when speaking English, without trying to mimic speakers born elsewhere.
Acquiring a New Accent
Many factors may affect a choice to acquire some particular accent.
Some may be motivated by the social perception of a prestige accent, one historically favored by some privileged group, and considered to represent elevated social status. Historically, RP and GA are the prestige accents of England and the United States. However, their role in each society is not the same. While up to two-thirds of US-born speakers may use GA, it is unlikely that more than one-tenth of English-born speakers naturally use RP.
Some may learn a certain accent to avoid being the target of bigotry, or to relieve anxiety about feeling foreign. Either is a worthy reason, but none is essentially linguistic, and may relate to a problem that is better resolved by other means.
For most, being understood is the essential concern. Flexibility with respect to specific habits, not complete transformation, may have the most practical benefit. Some may seek to acquire a specific accent, however, and doing so is a deeply personal choice, according to taste, objectives, and principles.