Kinda just realised that Samus was rescued by the Chozo when she was like three, or a little older than that, there's no chance her first language is still English or any other human language.
Any word in English that wouldn't be known to a three year old (and many that would be known to a three year old as well, as she'd just forget from years of disuse), she'd have to learn as an adult just before or after leaving Zebes.
Obviously, she's very smart, so grammer wouldn't be a problem for her, but it'd make sense she speaks very stiff and formal, maybe with issues of pronounciation if she'd only ever seen a word written but never heard it.
Inevitably she'd have to learn to write, or at least type, in English, but it's probably a chore for her. If she keeps a journal, she probably writes in Chozo
Higgs: Hey, stranger! Long time, no see!
Samus' internal monologue: I'm glad to see Anthony again, but wait, what does 'stranger' mean, again? Thing that makes another thing strange? No, hang on, he means 'outsider', 'unknown person'. He's joking, obviously.
Samus: It is good to see you, Anthony.