In Malaysia, I’ve been able to get away with wearing long shorts (slightly longer than knee length), t-shirts with a modest neckline that are not overly tight, and the like.
This is fine actually! Whatever you may have read in news, people are still free to dress in shorts and t-shirts. There may be mutterings from conservative locals, and I can’t promise you won’t get stared at, but generally you would be okay especially if you are in the modern shopping areas.
If you are visiting any mosques, then yes, do keep the long-sleeved shirts and full-length trousers or skirts handy. At the major mosques, you might be given a robe to cover up.
If you need more assurance, you can search popular social media platforms for pictures located in Brunei. For example, a third party Instagram tool for browsing photos by location such as Whatsthere, or perhaps Foursquare photos such as these photos taken at the Bandar Seri Begawan waterfront. I can look for more examples later if that would help.
Source: Bruneian living in Brunei
Credit:stackoverflow.com‘