My beta reader claims he'd never heard of the word 'conscript' before, and another buddy of mine said the same thing (both speak EXCELLENT English, but are not native to English speaking countries. One studied in the UK and the other in America (just saying so you guys know their English is not lacking)). My beta reader also says the word 'alloy' is obscure, are these words I should avoid/tiptoe around or is this just THEIR problem?
Not obscure at all. Sure, they only come up in certain circumstances, but they're common enough that I would expect a native speaker to know them in and out.
Yeah, those words are not obscure at all. They are not too commonly used, since the motive for either of those two words to show their faces is rather specific, but this is not the same as obscure. Neither would raise an eyebrow for me.
Tip for ya: just because their English is excellent, and I believe you, doesn't mean they'll necessarily know the words required for fiction. It only depends on what kind of English they've been exposed to. My husband's Czech and we met at a UK university - he has a bachelor's and masters both from the UK and his level is near-native. When it comes to business English and formal writing, he writes better than me! It's so good that when I proofread his stuff, either I only find very minor mistakes, or else I'm actually not sure how to write it myself cus the meaning's very complex, or other times it's so close to being right that I don't trust my own judgement. That's how good it is. And he'll ask me: what does "twirl" mean? Other words he might not know: supple, languid, sheer, decadent, awry, tether - I could go on. There've been more than one occasion when I would be reading something I wrote to him and he'd only tell me after I'm done that he'd stopped listening. When I got offended and asked him why, he told me there were too many words he didn't understand. Every line there was another word, usually a verb, to the point where the paragraph lost meaning. I've learnt from experience what sort of words he likely wouldn't know and these days when I come to such a word, I stop and I double check. Sometimes he does know it against my expectations, but usually he doesn't. (and this is someone who reads newspapers and academic textbooks without problems) In short, don't rely on foreigners' experience when it comes to whether a word is actually obscure, unless they're translators, writers in the language in question, or else well-read in your genre.