Literal translations don't teach you how a sentence actually sounds

Every language app I tried gave me one answer and moved on. That works until you're composing a work email in French and you genuinely don't know whether you're being too cold or too familiar — and there's no signal in a single translated string. The sharper problem is audio. Written French doesn't show you vowel length or liaison patterns. Written Japanese doesn't show pitch accent. You can memorize a sentence perfectly and still hear a native speaker say it in a way that doesn't match what you