The theme of this article is writing rules for an international audience. If it were just writing rules ingeneral, I could have pointed out that I already broke one rule about keeping headlines short. Which illustrates my point that, yes there may be truth to those old writing rules you see being knocked about in books and on the net. Nevertheless, sticking doggedly to those truths may uneccessarily limit your ability to connect to your audience.
1. Keep the vocabulary to 5th-grade level
It's true in general that you shouldn't get too sophisticated with your choice of words when writing for an international audience. On the other hand, you don't always have to limit yourself. If a word makes sense within the context of the sentence, readers will understand it even if they're not familar with the word.
For example, if a sentence said. "The proofreader was meticulous," and you werent' familiar with the word, "meticulous," you'd have little chance of understanding the sentence. If, however, the sentence read: The proofreader had a meticulous eye for detail, it would be clear what was meant.
2. Shun humor like the plague
We're often told to avoid humor when writing for an international audience. In addition to the culture issue, this gets mixed up with tone-of-voice. When writing business copy, especially B2B, you want to come off as serious and professional. But that doesn't mean there's never any room for humor.
Nevertheless, there is the issue of whether something that is funny for one national mentality tickles the funny bones of people in another country just as much -- or whether the humor is culture-specific. Yes, it is a dangerous game.
Still, I don't think you shouild shun humor altogether. You should avoid puns and difficult wordplay with an international audience -- especially if the text needs to be translated.
Yet there's no reason you can't use some humor when the business situation doesn't clearly exclude it. The Berlitz language school went so far as to make fun of Germans in this hilarious classic ad. It went viral, and as far as I know, it didn't insult any Germans. (Contrary to popular belief, they can take a joke).
Yes, you have to be careful with humor. I think to avoid it altogether, however, means you're both discounting its often universal nature and underestimating the human side of serious business.
3. Avoid conversational English
I've said it before, and I'll say it again: your web text -- no matter how formal -- should have some level of conversational tone to it. (See my article: The right tone of voice for business writing: Conversational!).
I recently read an article where the author advised against using a conversational tone when writing for an international audience. The example given was that he had used the phrase, "second to none" in a brochure, and his customer didn't understand it. In fact, she thought it meant, "average".
I would argue that it is impossible for a native speaker to detect that an everyday phrase such as this is not familiar to a non-native speaker. The only way to catch such an issue is via feedback, and even then, it would be a good idea to check with more than one non-native speaker.
Yes, it's important to use sophisticated vocabulary, humor and idiomatic (seemingly untranslatable) phrases with caution when writing for an international audience.
Yet if you second guess and censor yourself at every turn, you're going to end up with some pretty dull copy. By trying to connect to everyone, you'll end up connecting to no one.