Yes tax
although that will be less of a factor going forward presumably. The fact that Ireland is the only English-speaking country in the Euro currency (and if Brexit happens the EU as a whole) is also a big factor.
Facebook is to spend US$218m (£153m / €200m) on its second data center in Europe. Mark Zuckerberg's firm has promised an "innovative, environmentally friendly data center." It is easy to view the construction of this particular Facebook's answer to the expiration of Safe Harbor last year, to throw up a repository within the …
Your point is?
Is the population speaking English is f*** irrelevant. The question for a multinational company is "is the workforce speaking English?".
That in computing and telecoms equates to No in France, Meah, maybe in Germany, Spain, Italy and Portugal (*) and a resounding YES everywhere else in Europe.
This _INCLUDES_ Ireland - while English has an official status, it is officially the second language. First one is Irish.
While tax is a major factor tax is not the only one and the locations of data centers and research facilities in Europe are indicative of that. If it was just tax nobody would have put anything in Scandinavia or Switherland. That as we know is not the case.
OK, I'll bite. Ireland is an English-speaking country, for all intents and purposes. Irish might be the first official language (according to the constitution), but after having Irish forced down your throat for 13 years of school, most of us couldn't manage to string a sentence together, apart from "An bhfuil cead agam dul go dtí an leithreas?", and possibly the words of the national anthem, but that's about it.
It might have improved in recent years. I wouldn't know: finished school in 1993, emigrated in 2002.