In selecting foreign markets, you need to limit yourself to English-speaking countries (unless you are fluent in other languages). But even though they speak English in England, you need to recognize and honor the differences in spelling and terminology. Avoid American slang or jargon that shouts “America.” You will also need to weed out any references to American history, organizations, statistics, etc.
Because you have likely only sold North-American serial rights to articles sold in the states, you are free to sell them in other countries (except Canada—which is still in North America). Also, if you are submitting the same article in several different countries, it is still not considered a simultaneous submission, because each query is going into a different market.
When mailing to foreign countries, find out the proper amount of postage and how long it will take for delivery—either by air mail or by surface. Figure those times into your calculations when determining how long you should wait before following up on a submission. Also keep in mind that foreign countries may have poor postal service or are subject to postal strikes which may slow down the process considerably. Never put U.S. postage on your SASE. (See Foreign Mailing). Of course, you can avoid all the mailing headaches if the publisher is open to receiving e-mail queries and submissions.
There may also be some problems with understanding pay rates and foreign exchange rates. For example, in selling to Canada, you may be told that they will pay you $100 for an article, but they will mean $100 Canadian, not U.S. currency. So with the exchange rate you may make about $75 U.S, or less. Some foreign markets will pay in U.S. dollars if you ask. Some U.S. banks charge to cash foreign checks and even charge you a fee if the money is wired to your bank here, so check out applicable fees at your bank and determine the best way to handle such payments.
One more consideration with foreign sales is the tax ramifications. Always claim the foreign income, although the foreign publishers aren’t likely to report it or send you any form verifying what they have paid you during the year. It will be a good idea to make a habit of keeping copies of everything, including checks, from foreign markets.