The national language is called Bahasa Melayu (translated: Malay language), while English and Mandarin Chinese are widely spoken.
Essentials:
Same words in Malay: Teksi (taxi), restoran (restaurant), hotel (hotel), toilet (toilet), bas (bus), tren (train), shopping (shopping), kamera (camera) you get the picture.
Manglish is a local patois, informal speech mixing Malay, English, Hokkien, Mandarin, Cantonese and Tamil (also mangled English).
Malaysia is comprised of three main ethnic groups:
Other minority groups can fall under category of Bumiputera "son of the land", to include indigenous peoples, ethnic Thai, Khmer, Cham, and Portuguese Kristang (descendants).
Malaysia has a secular government with Islam as the official religion. As a diverse and multicultural country, it is also one of the countries with high religious diversity according to Pew's Global Religious Diversity Index.
According to 2010 census:
In terms of clothing, Asia tends to be more conservative in general, with the exception of large metropolitan cities. When visiting sacred sites or house of worship, you will be asked to wear modest attire. At certain touristy temples or mosques, pants/skirts/robes will be made available for borrowing/rental. Also broad generalization but Asia tends to have more superstitious folks too.
See food section