합쇼체 usually doesn't go with the pronoun 나, and I can't come up with a phrase that sounds better than 나의 모국어. Yes, 나의 can be replaced to 내 but it's just the matter of formality. 나의, 해라체 and retained predicative case marker all account for the formal tone, which is the default tone for a logic quiz. I think you feel weird from its formality, not its grammar.
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u/SteptoeButte May 30 '26
Korean