what are its ethnic groups?
Javanese, along with the Sundanese, Malay, and Batak.
Indonesia
he Javanese are the largest ethnic group, constituting 40.2% of the population, and are politically dominant. They are predominantly located in the central to eastern parts of Java and also sizable numbers in most provinces. The Sundanese, Malay, Batak, Madurese, Minangkabau and Buginese are the next largest groups in the country. 
what is the allah jang pasoe? It is a 1919 stage drama from the Dutch East Indies. what is the plot? It is about two brothers, who learn that money (the titular false god) is not the path to happiness. who wrote it? Kwee Tek Hoay do you know who the actors are? UNANSWERABLE when was it released? It was enacted in 1919 has the writer written other works? "Boenga Roos dari Tjikembang" and "The Victim Yi Yong Toan" you mentioned a place from where the play is from, what is the name of it in today's modern world? Indonesia how is the weather here? It has a wet season and a dry season, with no extremes of summer or winter. which tourist places can you find here? The  Komodo National Park and the Sawahlunto Coal Mine, the old towns of Jakarta and Semarang, and the royal palaces of Pagaruyung etc. what is the population? 237.6 million in 2010. which languages are spoken? Indonesian is the official language which religions are followed? Islam, Protestantism, Roman Catholicism, Hinduism, Buddhism, and Confucianism
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Indonesia [SEP] Ethnic groups and languages
A sense of Indonesian nationhood exists alongside strong regional identities. The country's official language is Indonesian, a variant of Malay based on its prestige dialect, which for centuries had been the "lingua franca" of the archipelago. It was promoted by nationalists in the 1920s and achieved official status under the name "Bahasa Indonesia" in 1945. As a result of centuries-long contact with other languages, it is rich in local and foreign influences, including from Javanese, Sundanese, Minangkabau, Hindi, Sanskrit, Chinese, Arabic, Dutch, Portuguese and English. Nearly every Indonesian speaks the language due to its widespread use in education, academics, communications, business, politics, and mass media.