Hi! The official name of the Melaka and George Town WHS is "Melaka and George Town, Historic Cities of the Straits of Malacca". But the last time I checked the encyclopedia, there is only one Strait of Malacca. So the descriptive appendage should just read "Historic Cities of the Strait of Malacca". Is this politically correct, or is the "Straits of Malacca" permissible, as in the "straits" collectively refer to the other bodies of water in the area, like the Singapore Strait, Strait of Johor, etc.?

Interesting question - it is one of those English words one uses without questioning its forms and origin (which is French - "Etroit")!
Whether a single narrow passageway of water is called "Strait" or Straits" seems to be a matter of common usage in different places rather than because of different meanings (e.g how "long" or "narrow" the body of water is). In many cases alternative usages for the same body of water are very/quite common. Some are (nearly) always "Strait", others (nearly) always "Straits" and some are frequently alternatives. The "plural" form seems to be used mostly in the format "Straits of xxxxxx" e.g Straits of Gibraltar, Straits of Magellan but not always - e.g Strait of Dover - but, just to break even that "rule" you can get "Dover straits"!
As regards Melaka etc - The British called their "colonies" in the area "Straits Settlements" (and issued wonderful old stamps with that title!) which related to the more normal form of "Straits of Malacca" (but there are also other usages - Strait of Malacca or Malacca Strait or Malacca Straits) upon which the original ones sat down the West coast of Malaya - including Singapore which also faced Johore across the Strait of Johore or Straits of Johore or Johore Strait or Johore Straits and the Riau Archipelago, Indonesia across the Strait of Singapore or Straits of Singapore or Singapore Strait ( The only examples of Singapore Straits I could find were the "Singapore Straits regatta" and Singapore Straits Times - but the latter refers I suspect just to the Singapore version of the Straits Times newspaper??)!!
As far as I know other languages do not have the same approach to the plural form for their equivalent word - can any French, German, Spanish or Dutch etc speakers confirm this?? Nor have I been able fully/satisfactorily to establish why/when this "plural" form was adopted in English - does anyone know? It occurs to me that another English word for a similar geographic entity is "narrows" (as in Verrazano Narrows") - This too can be stated in the singular i.e "A Narrow" but far less frequently. So the dual use of singular and plural forms for describing the same thing seems to exist whether the word is Romance or Germanic in origin.
Those of you struggling with achieving perfection in use of English might also care to consider whether "Straits" or "Narrows" are singular or plural - as far as I am aware the use of a singular verb is perfectly correct as in "The Straits of Malacca is one of the busiest sea lanes in the World" - this because there is only 1 of them (it??)!!

Well, on another note, aside from Melaka and George Town, lots of WHS have increasingly been using descriptive phrases as part of the official names. China has used it in its 1998 inscriptions, although the descriptions seem to focus more on the sites' location in Beijing rather than on their outstanding universal value. France has lately been using such an approach too. From Provins, to Le Havre, Bordeaux, New Caledonia and saltworks extension. Although in the case of Bordeaux, the description has nothing to do with its outstanding universal value but just the place's nickname. Spain has also tried such an approach, although not successfully, in 2000. But the advisory body recommended that the descriptions be removed, lol... probably an overkill in descriptions used.