getDayTranslations.ts

function getSupportedLocales(): string[] {
	const candidates: string[] = []

	const letters = Array.from({ length: 26 }, (_, i) => String.fromCharCode(65 + i))
	for (const a of letters) {
		for (const b of letters) {
			candidates.push(a + b)
			for (const c of letters) {
				candidates.push(a + b + c)
			}
		}
	}

	return Intl.getCanonicalLocales(Intl.DateTimeFormat.supportedLocalesOf(candidates))
}

let locales: string[]

/**
 * Get the translation of a day in every Intl-supported locale
 * 
 * @param day 1=Monday ... 7=Sunday
 * @returns A set translations of the given day
 */
export function getDayTranslations(day: 1 | 2 | 3 | 4 | 5 | 6 | 7) {
	locales ||= getSupportedLocales()
	const result = new Set<string>()

	const date = new Date()
	date.setDate(date.getDate() + (day + 7 - date.getDay()) % 7)
	const format = { weekday: 'long' } as const

	for (const locale of locales) {
		const dayName = new Intl.DateTimeFormat(locale, format).format(date)
		result.add(dayName)
	}

	return result
}