It is hardly a revelation that the English language currently dominates online. The internet was created in 1969 in the USA and the world wide web was created by a Brit 20 years later. Thus, not surprisingly English is used by 42% of online users with a growth of 280% since 2000. Perhaps a good indication of modern trends, at least in the West, is that the #1 language on Facebook is English, with over 52%.
However, this is set to change. Mandarin is the most widely spoken native language in the world and is used by 33% of people online. This has undergone a growth of 1,280% over the same period. And, don't forget, it was only this year that Chinese characters were finally approved for the creation of domains. Expect a catch up soon.
The language usage in the EU, on the other hand, is more diverse with 23 official and working languages although due to time and budgetary constraints, the European Commission generally employs English, French and German reflecting general usage. In fact, roughly 13% of EU citizens speak English as their first language (mainly in the UK and Ireland) with a further 38% having sufficient knowledge of English to have a conversation. Therefore, it's not surprising that an attempt to have French recognised as the official legal language of the EU failed a couple of years ago. And now a (Flemish-speaking) Belgian MP is stirring things up by calling for the EU to use English.
When it comes to doing business or politics then maybe English is the natural choice in the West and Mandarin in the East. When it comes to socialising with your friends online, you'll communicate in your own language, of course. But does it matter if you're buying online? You can tell from the photos and maybe an internationalised description what you're buying but, apart from the lawyers - me included - nobody reads website terms anyway.