UNESCO or Unesco?
A quick mention for a couple of 'style guides' that are very helpful when trying to navigate the finer points of correct writing in English...
Two well-known British newspapers, the Guardian and the Economist*, have for many years published style guides containing their own sets of rules on issues such as the use of capital letters and acronyms, along with lists of frequently misused words and advice about the differences between British and American English.
Conveniently, the Guardian's style guide is available for free online.
Inevitably there are a few differences of opinion between the two guides, for example regarding acronyms: the Economist's 'UNESCO' becomes 'Unesco' in the Guardian.
It just goes to show that when you get into the minutiae of writing in English, different approaches exist and there is no single, definitive set of rules.
*You might think of The Economist as a magazine but it likes to describe itself as a 'newspaper'.