There's loads of non-English documentation, open source and otherwise. The quality is usually not bad. Like everyone says, many languages let you put Unicode in

There's loads of non-English documentation, open source and otherwise. The quality is usually not bad. Like everyone says, many languages let you put Unicode in identifiers. I've never actually seen anyone do that. I've seen Unicode in comments, or foreign words romanized to [A-Za-z] for identifiers. For a high-end customer-facing role involving complex business logic, you probably need something close to native ability. I've seen (and hired) lots of developers with B2 or worse English doing mathematical stuff. Their language skills were an impediment, but not a serious one.