That's an interesting topic.
But my first thought is, this is the age of the Internet. Even if your game were delivered as a compiled binary with military-grade encryption, as soon as somebody figures out what the achievements are, they'd be posting a YouTube video about it or describing it on a wiki somewhere. And anybody who wanted to find out would just google it, and find the answer far more easily than reading through the code.
So, I probably wouldn't bother trying to hide it. Most players won't go looking for answers, and if somebody does, I'd rather have them read code than read a wiki page anyway. 🙂
On the other hand, maybe encrypting the strings might be worth a small amount of effort, for a small amount of spoiler prevention.