Europe is to some extent a special case - even outside of software, English is the pan-European lingua franca; lots of college-educated people know a lot of it

Europe is to some extent a special case - even outside of software, English is the pan-European lingua franca; lots of college-educated people know a lot of it even before getting into tech. In places like China, or Central Asia, or the Middle East, this is not as much the case, and so picking up English skills add a further barrier to entry to the field. (Europe is only a special case "to some extent" because English also competes for lingua franca status with Hindi in India; in Japan it's taught (badly) as a result of connections with the US; and in countries as varied as Israel and Singapore it has a foothold.) If you're starting from first principles, and are willing to go with that common-second-language threshold instead of insisting on people's first languages, English is still definitely a clear first choice - it barely edges out Chinese for total L1 + L2 speakers, and those speakers are concentrated in the centers of software development. After that you have Chinese and Hindi (both fairly restricted in geographical reach, but involving lots of people), then Spanish (most of Latin America) and French (spoken in a dizzying array of cultures as L2, because of colonial history in Africa and the Middle East). And then you finally get to Arabic :-P