Indonesian is the official language of Indonesia and is spoken by over 230 million people. Malay, one of the official languages of Malaysia is also mutually intelligible with Indonesian, so it is not included on this list. Indonesian is a member of the Austronesian language family. According to the eLinguistics.net analysis using specific software modules to assess linguistic relationships, the five languages most similar to Indonesian are Minangkabau, Acehnese, Kangeanese, Madurese, and Balinese.
- Minangkabau (75.0)
The Minangkabau language is predominantly spoken in West Sumatra, Indonesia. Minangkabau shares a high degree of lexical similarity with Indonesian, with many words being easily recognizable to Indonesian speakers. It has similar phonetic characteristics, though there are notable differences in vowel pronunciation and the presence of distinctive Minangkabau consonants. - Acehnese (67.6)
Acehnese is primarily spoken in the province of Aceh at the northern tip of Sumatra. Although Acehnese has been influenced by Arabic, it still shares a considerable number of words with Indonesian. However, Acehnese has unique phonological features, such as the use of implosive consonants, which are not found in Indonesian. - Kangeanese (65.3)
Kangeanese is spoken on the Kangean Islands, east of Madura, Indonesia. Kangeanese shares many common words with Indonesian, though it also has distinct local vocabulary. The phonetic system of Kangeanese is quite similar to that of Indonesian, with minor variations in pronunciation. - Madurese (59.6)
Madurese is commonly spoken on the island of Madura and the northeastern coast of Java, Indonesia. There is a significant overlap in vocabulary between Madurese and Indonesian, particularly in basic and everyday terms. The syntax and morphology of Madurese are quite similar to Indonesian, although there are unique elements that distinguish the two. - Balinese (46.8)
Balinese is natively spoken on the island of Bali, east of Java. Balinese shares a substantial number of words with Indonesian, although it has less similarities than other languages on this list. Still, the grammatical framework of Balinese is quite similar to Indonesian, though it includes a more complex system of honorifics and social registers.
(to be considered for the list, the language must be spoken by at least one million people)