Sundanese

Across the Indonesian provinces of West Java and Banten, where the Sunda people are the majority. Bandung is the largest Sundanese-speaking city. Sundanese coexists with Indonesian (the national language used in education and formal contexts) and is the everyday language at home and in informal settings throughout the region.

No. Both are Austronesian languages of Java, but they belong to different branches (Sundanese is closer to the Indonesian-Malayic group; Javanese is in its own subgroup) and they're not mutually intelligible. They share many cognates and similar speech-level systems, plus heavy contact-based vocabulary overlap, but a Javanese speaker can't follow Sundanese conversation without study, and vice versa.

Three main levels — informal, neutral/middle, and formal/refined — with vocabulary that shifts entirely as you move between them. The system is somewhat lighter than Javanese, with fewer levels and less aggressive vocabulary swap, but still socially significant. Choosing the wrong level for the listener marks the speaker as rude, careless, or under-educated.

An abugida descended from earlier Indian-influenced scripts of the archipelago, with letterforms that look related to Javanese and Balinese scripts. Aksara Sunda was largely displaced by the Latin alphabet during the Dutch colonial period and is now used mainly for cultural signage in West Java, in modern revival contexts, and in academic publication. Daily writing is overwhelmingly in the Latin alphabet.

Both are Austronesian. Sundanese has more elaborate verb morphology, the speech-level system, and distinct vocabulary that doesn't overlap with Indonesian for many basic words. Indonesian is the national lingua franca of education and media; Sundanese is the heritage and intimate language of West Java. Most Sundanese speakers are bilingual in both.