Absolutely yes. Virtually every relevant and up-to-date resource out there is in English. Stack Overflow, GitHub repos, documentation, official specifications,

Absolutely yes. Virtually every relevant and up-to-date resource out there is in English. Stack Overflow, GitHub repos, documentation, official specifications, technical articles, tutorials and blog posts, podcasts, videos. English is the lingua franca of the community. You need to be able to: A. Read and understand an enormous amount of written material on complex matters in English with no more effort than you'd expend reading in your mother tongue and B. Produce clear, concise and elegant prose in order to engage with the community (not to mention your coworkers!), learn and exchange ideas. I could hardly take seriously a software developer (or scientist, researcher, teacher for that matter) who has poor English.