The official languages of India are Hindi and English.
That said, each region has its own language such as Urdu, Gujarati, Punjabi, and Bengali.
India is known for its four world religions that include Hinduism, Buddhism, Jainism, and Sikhism, which all originated here. Islam and Christianity are also practiced in India, but over 70% of the population are Hindu.
Celebrations are held in India almost all year round in keeping with the Hindu, Sikh, Buddhist, Jain, and Muslim festivals. As such pretty much whenever you choose to go you will find some kind of celebration or other. For many travelers, these are the highlight of a trip here as they are often colorful, noisy, and visitors are almost always welcome.
There are too many celebrations to list but some to look out for should you be in the country at the right times include Pushkar Camel Fair in November, Puri Rath Yatra festival, usually held in June or July, and the Hemis festival in Ladakh. Many festivals in India follow the phases of the moon and thus are planned according to the lunar calendar and Muslim holidays run alongside the Islamic calendar and the dates often change every year.