Summary: Users from other countries have special needs related to entry fields for names and addresses, measurements and dates, and information about regional product standards.
To support international users, you should ideally have special sites in various languages. If you can't produce such localized sites, you should at least conduct user testing in each of your important target countries to ensure that your main site is fairly easy for your foreign customers to use. The guidelines have always stated as much, but if your company is typical, I know you won't comply.
Even though many companies do half their business overseas, experience shows that few companies are willing to pay the high cost of testing in multiple countries. We're lucky if a company invests in domestic testing; let's not push our luck too far.
Here instead are the minimum requirements for ensuring that international users can use your site. Just remember: To fully maximize your business potential in other countries, you should do much more.
Names and Addresses
Nothing is more humiliating than seeing the phrase "illegal name" after typing your name into a website form. What do you mean, illegal? That's my name! Accommodating both common and variable name spellings is an extremely important guideline.
Also, in many Asian countries, the first name is the family name, so it's best to offer a single field to accommodate a person's entire name. Offering separate fields for first name and last name is a prescription for confusion. In some countries, people have only one name, so two fields would stump them as well.
Ideally, your site supports Unicode and double-byte characters, which are required for many Asian languages. But at a minimum, accept an extended character set that goes beyond plain ASCII. You want to allow shipments addressed to, say:
Åle Allé 7
As the example shows, extended character sets are required for the street address. You also need to accommodate house numbers that follow street names and ZIP codes of various lengths that precede city names. In fact, it's better to refer to "postal code/ZIP code" instead of just ZIP code, which is a U.S.-only term.
For phone numbers, allow for international numbers containing a varying number of digits and a country code. Also, avoid stating your own phone number in letters (say, 1-800-TOO-EASY) because many countries don't include letters in their telephone keypads.
Measurements and Dates
Give measurements in both the metric system and traditional English units. For example, the size of the Canon Powershot S2 digital camera is 4.4 x 3.1 x 3.0 inches or 11.3 x 7.8 x 7.5 cm. Depending on your country, having only one set of measures would render you incapable of visualizing the camera's size.
Similarly, provide temperatures in both Fahrenheit and Celsius. If you're planning a Stockholm visit and a website tells you that the weather forecast calls for a high of 20 degrees, should you pack t-shirts or your warmest coat? If it's 20°C (68°F), t-shirts are a good bet, though they're unlikely to serve you well if it's 20°F (-6°C). Offering temperatures in both standards accommodates all users. At very least, be explicit about which measurement you use.
For dates, the main guideline is: Always spell out the name of the month. Using a notation like 8/9 is confusing -- is that August 9th or the 8th of September? If you write "Aug. 9" people from all countries will understand it, and it requires only a few more characters. Far better than having customers show up at your hotel thirty days before or after their actual reservations.
Regional Product Standards
Above all, clearly state whether your product is only available in certain countries or will only function in certain countries. Electricity standards vary around the world. The most common are 110V and 220V; you won't be popular if you sell something that'll fry the moment it's plugged in. Similarly, video standards vary, and most DVDs are artificially restricted to play only in a few countries.
Conversely, if you have a multistandard product, explicitly say so. Assure users that the product will work because it has a universal power supply, for example, or because it's a DVD without limited "regional coding." Although most users are unaware of such differences, those who are aware of them won't buy your product unless you tell them that it'll work in their country.
Remember, these guidelines are only the most necessary requirements for internationalizing your website. Follow this advice, and you'll get business from international customers. To get more business, start doing user testing abroad.