South America – There doesn’t seem to have been much published on 20th century postal rates and without this information “writing up” covers is almost impossible. Although it might be possible to locate Post Office Guides that would tabulate this data I assume they would have been written in Spanish or Portuguese neither of which I speak. On the plus side there is a reasonable quantity of material available and, I assume, relatively little competition for it since most of the auction lots I examined had attracted no bids.
Colonial Africa (the non-English speaking parts) – Information does exist on the postal history of French West Africa but I imagine that the quantity of mail coming out of these countries is relatively small which, to me, would imply that that anything other than the first-tier letter rate covers would be in short supply and highly prized (and priced). At least I do understand enough French.Eastern Europe – Language is the main barrier here. Logic dictates that substantial quantities of 20th century postal history must exist but without the skills required to decipher postal marking differentiating the common from the scarce and rare seems too big a challenge. It certainly isn't impossible that I might do a more detailed survey of what is available sometime in the future.
Scandinavia – I’m prepared to bet that somebody somewhere has published information on postal rates but again my poor language skills are a major barrier.