nested object keys type

nested_object_key.ts

const locale = {
    'en_us': {
        hello: 'hello',
        greetings: {
            morning: 'Good Morning',
            evening: 'Good Evening',
			else: {
				foo: 'bar'
			}
        },
    },
} as const;

type LocaleMap = typeof locale;

type LocaleKeys = keyof LocaleMap;

const current_locale: LocaleKeys = 'en_us';

type LocaleType = LocaleMap[LocaleKeys];

type Values = string | number | boolean | null | undefined;

type PathInto<T extends Record<string, any>> = keyof {
    [K in keyof T as T[K] extends string
        ? K
        : T[K] extends Record<string, any>
        ? `${K & string}.${PathInto<T[K]> & string}`
        : never]: never;
};

function t<T>(key: PathInto<LocaleType>): string {
    return locale[current_locale][key];
}

t('hello');

taken from this Youtube Video by Tech Talks with Simon