Commonwealth English is the name for a mythical variety of English
which is only defined as “not U.S.”, and ignores the fact that the Commonwealth of Nations is an international organization whose membership changes regularly.
There is no such distinct variety defined by either accent, vocabulary, or spelling and orthography. English within the Commonwealth of Nations is diverse – for example, Canadian English
is more closely related to (U.S.) American English
than to any other variety – while English dialects can cross the bounds of the Commonwealth, like Irish English, spoken in the Republic of Ireland which is left the Commonwealth a half-century ago, and in Northern Ireland a part of the United Kingdom, a charter member of the Commonwealth of Nations
Here in Ottawa we speak and write Commonwealth English, same as in Auckland, Karachi, London, and Singapore.