Question: Why did Calcutta change its name?

Renaming of cities in India




The renaming of cities in India started in 1947 following the end of the British imperial period. Several changes were controversial, and not all proposed changes were implemented.  Each had to be approved by the central government in New Delhi.
The renaming of states and territories in India has also taken place, but until recently with actual substantial name changes in both local language and in English such as the old British state name of Travancore-Cochin to Kerala (1956). The most notable recent exceptions are Indian English spelling-changes of Orissa to Odisha (March 2011)[1] and the Union Territory of Pondicherry (which includes the City of Pondicherry) to Puducherry.
Renaming in local languages
In the post-colonial era, several Indian states' names were changed. Some of these changes coincided with the States Reorganisation Act of 1956, a major reform of the boundaries of India's states and territories that organised them along linguistic lines. At this time, for example, Travancore-Cochin was renamed Kerala. Later state name changes include the reorganisation of Madhya Bharat into Madhya Pradesh in 1959;[2] and the renamings of the Madras State to Tamil Nadu in 1969, of the Mysore State to Karnataka in 1973, and of Uttaranchal to Uttarakhand in 2007.
Name changes have varied with respect to the levels of language at which they have been applied, and also accepted. Some of these local name changes were changes made in all languages: the immediate local name, and also all India's other languages. An example of this is the renaming of predominantly Hindi-speaking Uttaranchal (Hindi: उत्तराञ्चल) to a new local Hindi name (Hindi: उत्तराखण्ड Uttarakhand). Other changes were only changes in some of the indigenous languages. For example, the renaming of the Madras Presidency to Madras State in 1947 and then Tamil Nadu in 1969 required non-Tamil speakers to change from an approximation of the British name (Tamil: மதராஸ் மாகாணம் Madras Presidency, then  Madras State Tamil: மதராஸ் மாநிலம்) to a native Tamil name (Tamil: தமிழ்நாடு Tamil Nadu, "Tamil land").
In general, changes to the local names of cities in the indigenous languages are less common. However, a change in English may sometimes also be a reflection of changes in other Indian languages other than the specific local one. For example, the change of Madras (Tamil: மதராஸ் Madras) to Chennai (Tamil: சென்னை Chennai) was reflected in many of India's languages, and incidentally in English, while the Tamil endonym had always been Chennai and remained unaffected by the change. Similarly, Bombay, which was always called 'Mumbai' in Marathi, was restored to Mumbai in 1996.
Renaming in English
Change in official English spelling
The renaming of cities is often specifically from English to Indian English in connection with that dialect's internal reforms. In other words, the city itself is not actually renamed in the local language, and the local name (or endonym) in the indigenous languages of India does not change, but the official spelling in Indian English is amended. An example is the change from English "Calcutta" to English "Kolkata" – the local Bengali name (কলকাতা Kôlkata) did not change. Such changes in English spelling may be in order to better reflect a more accurate phonetic transliteration of the local name, or may be for other reasons. In the early years after Indian independence, many name changes were effected in northern India for English spellings of Hindi place names that had simply been romanised inconsistently by the British administration – such as the British spelling "Jubbulpore," renamed "Jabalpur" (जबलपुर) among the first changes in 1947. These changes did not generate significant controversy. More recent and high-profile changes – including renaming such major cities as Calcutta to Kolkata – have generated greater controversy.[3] Since independence, such changes have typically been enacted officially by legislation at local or national Indian government level, and may or may not then be adopted by the Indian media, particularly the influential Indian press. In the case of smaller towns and districts which were less notable outside and inside India, and where a well known English name (or exonym) could not be said to exist, older spellings used under British India may not have had any specific legislation other than changes in practice on the romanisation of indigenous Indian language names.
Realignment of the official Indian English name to an alternative local name
Aside from changes to the official English spellings of local names there have also been renaming proposals to realign the official name, hence the English name with an alternative local name. Ethnically sensitive examples include the proposals by the Bharatiya Janata Party (1990, 2001) to rename Ahmedabad to Karnavati[4] and Allahabad to Prayag. These two proposals are changes from the historically Mughal name to a Hindu native name. These can be represented as a change from Urdu language to Hindi language, but since the two languages are variants of Hindustani the proposal is effectively a cultural and ethno-religious proposal rather than a linguistic one.[5]
Adoption of name changes in India and overseas
Official name changes take place quickly if not immediately in official government sources.[6] Adoption may be slower among the media in India and abroad, and among Indian authors.[7][8][9]
Important examples

States
Travancore-Cochin → Kerala (1 November 1956).
Madhya Bharat → Madhya Pradesh (1 November 1959)
Madras State → Tamil Nadu (14 January 1969)
Mysore State → Karnataka (1 November 1973)
Uttaranchal → Uttarakhand (1 January 2007)
Orissa → Odisha (4 November 2011)
Cities
Notable city names that were officially changed by legislation after independence include:
Jabalpur (Hindi: जबलपुर), from Jubbulpore, respelled in 1947
Jajmau (Hindi: जाजमऊ), from Jajesmow, respelled in 1948 [10]
Kanpur (Hindi: कानपुर), from Cawnpore, respelled in 1948
Vadodara (Gujarati: વડોદરા), from Baroda, respelled in 1974
Thiruvananthapuram (Malayalam: തിരുവനന്തപുരം), from Trivandrum, respelled in 1991
Mumbai (Marathi: मुंबई), from Bombay, renamed in 1995[11]
Kochi (Malayalam: കൊച്ചി), from Cochin, respelled in 1996
Chennai (Tamil: சென்னை), from Madras, renamed in 1996
Kolkata (Bengali: কলকাতা), from Calcutta, respelled in 2001
Kadapa (Telugu: కడప), from Cuddapah, respelled in 2005
Puducherry (Tamil: புதுச்சேரி), from Pondicherry, renamed in 2006
Bengaluru (Kannada: ಬೆಂಗಳೂರು), from Bangalore, respelled in 2007 [12]
Belagavi (Kannada: ಬೆಲಾಗವಿ), from Belgaum in 2014 [13][14]
Tumakuru (Kannada: ತುಮಕುರು), from Tumkur in 2014
Hubballi (Kannada: ಹುಬ್ಬಳ್ಳಿ), from Hubli in 2014
Shivamogga (Kannada: ಶಿವಮೊಗ್ಗಾ), from Shimoga in 2014
Hosapete (Kannada: ಆಸ್ಪತ್ರೆ), from Hospet in 2014
Mysuru (Kannada: ಮೈಸೂರು), from Mysore in 2014
Kalaburagi (Kannada: ಕಲಬುರಗಿ), from Gulbarga in 2014
Chikkamagaluru (Kannada: ಚಿಕ್ಕಮಗಳೂರು), from Chikmagalur in 2014
Vijapura (Kannada: ವಿಜಪುರ), from Bijapur in 2014
Ballari (Kannada: ಬಾಲಾರಿ), from Bellary in 2014
Mangaluru (Kannada: ಮಂಗಲುರು), from Mangalore in 2014
Rajahmahendravaram (Telugu: రాజమహేంద్రవరం), from Rajahmundry in 2015
Gurugram (Hindi: गुरुग्राम) from Gurgaon in 2016
Prayagraj (Hindi: प्रयागराज), from Allahabad, renamed in 2018
Atal Nagar (Hindi: अटल नगर), from New Raipur in 2018
Ayodhya (Hindi: अयोध्या), from Faizabad in 2018
For others, by state order, see list of renamed Indian cities and states.
Alappuzha (Malayalam: ആലപ്പുഴ), from Alleppey
Baranagar (Bengali: বরানগর), from Barahanagore
Guwahati (Assamese: গুৱাহাটী), from Gauhati
Indore (Hindi: इंदौर), from Indhur
Kanchipuram (Tamil: காஞ்சிபுரம்), from Kāñci-pura And Conjevaram
Kannur (Malayalam: കണ്ണൂർ), from Cannanore
Kollam (Malayalam: കൊല്ലം), from Quilon
Koyilandy (Malayalam: കൊയിലാണ്ടി), from Quilandi
Kozhikode (Malayalam: കോഴിക്കോട്), from Calicut
Kumbakonam (Tamil: கும்பகோணம்), from ancient name Kudanthai
Mayiladuthurai (Tamil: மயிலாடுதுறை), from Mayavaram ancient name Mayuram
Narmada (Gujarati: નર્મદા), from Nerbudda
Nagaon (Assamese: নগাওঁ), from Nowgong
Palakkad (Malayalam: പാലക്കാട്) from Palghat
Panaji (Hindi: पणजी) from Panjim
Pune (Marathi: पुणे), from Poona
Ramanathapuram (Tamil: ராமநாதபுரம்), from Ramnad
Sagar (Hindi: सागर), from Saugor
Shimla (Hindi: शिमला), from Simla
Thalassery (Malayalam: തലശ്ശേരി), from Tellicherry
Thanjavur (Tamil: தஞ்சாவூர்), from ancient name Tanjore
Thoothukudi (Tamil: தூத்துக்குடி), from Tuticorin
Thrissur (Malayalam: തൃശൂർ), from Trichur
Tindivanam (Tamil: திண்டிவனத்தில்), from Tinthirivanam
Tiruchirapalli (Tamil: திருச்சிராப்பள்ளி), from Trichinopoly and its short form Trichy
Tirunelveli (Tamil: திருநெல்வேலி), from Tinnevelly
Tiruvallikeni (Tamil: திருவல்லிக்கேணி), from Triplicane
Udhagamandalam (Tamil: உதகமண்டலம்), from Ootacamund and its short form Ooty
Viluppuram (Tamil: விழுப்புரம்), from Vizhupparaiyar And Vizhimaa Nagaram
Varanasi (Hindi: वाराणसी), from Benares
Vatakara (Malayalam: വാടകര), from Badagara
Virudhachalam (Tamil: விருத்தாச்சலம்), from  Vriddhachalam ancient name Thirumudhukundram
Vijayawada (Telugu: విజయవాడ), from Bejawada
Visakhapatnam (Telugu: విశాఖపట్నం), from Waltair, and before that Vizagapatnam and its short form Vizag



Town names that derive from ancient names:
Mandi (Hindi: मंडी), derived from Mandav Nagar [15]
Nellore (Telugu: నెల్లూరు), in ancient times Simhapuri [16]
Proposed changes
Several other changes have been proposed for states and towns.
States and Union territories
Kerala to Keralam
West Bengal to Bangla
Cities
Bhopal to Bhojpal [17]
Hyderabad to Bhagyanagar[18]
Shimla to Shyamala[19]
Need for unification of spelling
India has various local languages. Even (Romanised) English spellings in long and wide use often vary depending upon which government department or agency uses them. To the point, a few examples are Quilandy vs. Koyilandy, Canannore vs. Kannur, and Rangiya vs. Rangia. Different departments of the government may have used official spellings in use at the time, while locations associated with Indian railways mostly maintained British-era spellings. The confusion inherent in such variations has often resulted in serious consequences like people having two "different" addresses (theoretically designating the same place) in their official records leading to legal disputes, or one house having residents of different house addresses due to differing place names. Many people argue that such confusion can lead to indeterminate and/or unintended consequences.[20]
See also

List of renamed Indian cities and states
List of renamed places in Pakistan
Renaming in South Africa



 by Nundo Lal Dey