Things to know about Kuala Lumpur
Kuala Lumpur is ostensibly a liberal city by Malaysian standards and wearing revealing clothes will rarely cause major problems. However, avoiding overly revealing clothes goes a long way towards blending in. Many mosques and temples require covering up, and you will get more respect from officialdom if you dress up a little. Many places of worship including all mosques will require you to take your shoes off before entering. When eating with hands rather than cutlery, do not eat with the left hand in public as it is considered impolite. If you can speak just a few words of the four main local languages, namely Malay, Chinese (especially Cantonese), Tamil and English, it will ingratiate you a lot with the locals. Also, while you may drink in pubs, restaurants and bars, public drunkenness is not tolerated. You will be more vulnerable to getting robbed or will find yourself in the back seat of a police car.
As befitting the nation's capital, Malay is universally spoken and understood by locals in Kuala Lumpur.
However, as Malaysia's largest city, Kuala Lumpur is also home to Malaysians of many different ethnic and cultural backgrounds, and this is often reflected in the number of languages that are used by locals in daily life. The lingua franca of the Chinese community is Cantonese, and most of the ethnic Chinese can speak Cantonese regardless of their native dialect, with a significant number also able to speak Mandarin. Kuala Lumpur is also home to many Indians, most of whom are native speakers of Tamil.
English is also widely spoken, and English-speaking tourists should generally not have a problem getting around.