Closed source is generally compiled code in an executable, so you'd have to do a lot of work de-compiling it back to the source code first.
Even at the OS level, lots of the stuff "under the hood" in Windows is obfuscated, and still the same issue, most of it is compiled code, you'd have to de-compile a significant portion of it (in an OS there's also an amount that doesn't have to be de-compiled) to be able to actually look at the code itself.
Please don't apologize for bad English, it's not against the law to have English as a second language. As a US citizen, one of the most frustrating thing is knowing brilliantly competent and capable immigrants who are ignored and passed over because their education and credentials are simply in a different language. They often come as refugees and didn't have the opportunity to get a great English education, but literally come with multiple degrees from quality universities in their home countries. Treating them like they know less because they speak a different language is so fucking absurd. Also, your English is fine, don't beat yourself up.
I would sound worse in any language I tried to speak other than English, you're doing better than I would, and better than a lot of English speakers would when put in the same situation speaking a second language they're not familiar with.