Imagine you run WordPress with English as default language, but some posts are in another language. Dutch, maybe? Up until a couple of months ago, you wouldn’t really notice anything about that setup. Google might be slightly confused, but us bloggers aren’t really into SEO anyhow, no? But with the release Safari 5.1, Firefox 16 and especially Internet Explorer 10, support for CSS Hyphenation became (somewhat) widely available and if your theme (WordPress TwentyTwelve or its performance-optimized 2012.FFWD child theme for example) has support for in the CSS, your hyphenation would yield weird results because of the fact that the browser uses the language attribute in the HTML to decide which dictionary to use.
The solution, if your theme is HTML5, is to add the lang-attribute to the article-tag if you have something to check the language with. In my case I just had to copy TwentyTwelve’s content.php and change line 11 into:
A real simple hack indeed; I check if the article has category “lang:nl” attached to it (which I already used) and set the language-attribute with the correct value if it does. Hyphenation now works for Dutch blogposts and I guess Google will be happier as well that way?