Languages
I just noticed something here. Not going to call this the typical "lazy writing" or "plotholes", but maybe just the writers forgetting certain elements of the character. I used to watch Magnum all the time when it originally aired, and for many years, I would watch the reruns as well. I haven't really watched much of the show in the last 15 years, but recently bought the whole box set with all of the seasons.
Going through season one right now and I'm on the third episode, China Doll. In it, he asks Mai Ling to speak English when she's talking to her uncle, but she states that her uncle does not speak English. Magnum then asks her if he speaks French or Vietnamese, to which she states no, only Chinese. I'm not sure if he was asking these because he spoke or at least understood those languages.
Later on in the series though, when Magnum is reunited with Lilly, he can't really communicate with her because she only speaks French and Vietnamese, to which he only knows a few words and phrases.