That phrase always makes me grin because it's one of those cheeky pop hooks that sounds so simple but carries a lot of attitude. If you strip it down to plain English, 'sweet but psycho' basically means someone who appears kind, charming, or innocent on the surface ('sweet'), but who also behaves in unpredictable, intense, or erratic ways ('psycho'). The literal, word-for-word translation would be something like "pleasant or nice, but crazy," but that misses the playful edge and the pop-culture nuance the original line carries.
When I think about translating the lyric meaning rather than copying the exact words, I tend to offer multiple shades: a neutral literal version — "sweet but crazy"; a softer, less stigmatizing option — "sweet but a little wild" or "sweet but unpredictable"; and a more dramatic rendition — "adorable yet dangerously unstable." Each choice shifts the tone: "crazy" is blunt and raw, "wild" feels flirtatious and fun, and "unstable" reads clinical and colder. If you were turning those lyrics into conversational English that keeps the song's playful vibe, I'd go with something like, "She's cute and charming, but a bit wild and unpredictable," which keeps the flirtatious, teasing energy without sounding like an insult.
There are also translation pitfalls to watch for. Using words that equate eccentric behavior with mental illness can be offensive, so many translators soften 'psycho' to avoid stigmatizing real mental health issues. In other languages people often choose culturally appropriate words that keep the balance of sweetness and danger — for example, in Indonesian you might hear "manis tapi sedikit gila" or a milder "manis tapi agak liar." I usually prefer the milder phrasing in conversation because it preserves the song's playful tease rather than making it clinical. At the end of the day, that line works because it juxtaposes two extremes — charm and instability — and nails a certain pop-star swagger. I still hum that chorus when I'm in a silly mood and it always makes me smile.