Even though the web is a global network, many businesses are happy to create an English-language site and leave it at that. In some cases, that’s fine. The burden of translation can be quite high, and if the market a site is addressing is fairly localized, then the ROI of internationalizing isn’t worth the effort. The US and Europe, most of the populations of which have at least a passing familiarity with English, have long dominated the online economy, but that’s rapidly changing.
South America, India, and China are quickly growing in online spending power, and companies that fail to address expanding markets are missing a trick. Sites that are targeted at the European market will generally find that their audiences speak English, but if they can find what they need on sites in their native languages, they’ll preferentially do business there, so the international nature of English shouldn’t be relied on.
Even within the US, providing multi-lingual sites is a good idea. The Spanish-speaking population is large, and with Mexico, and Central and South America close by, there’s much to be gained from providing at least bilingual content.