fix, feat: add currency conversion stub

uses proper JS api for currency formatting and preparations for showing other currencies based on page locale

src/content/utils/currency.ts

@@ -1,8 +1,47 @@
 import { conversion_ref_usd } from '../config';
 
+export function defaultCurrencyForPageLocale(locale: string): string | null {
+	switch (locale) {
+	case 'de':
+	case 'fr':
+	case 'it':
+	case 'nl':
+	case 'hu':
+		return 'EUR';
+	case 'ja':
+		return 'JPY';
+	case 'tr':
+		return 'TRY';
+	case 'da':
+		return 'DKK';
+	case 'pt-br':
+		return 'BRL';
+	case 'zh-hans':
+	case 'zh-hant':
+		return 'CNY';
+	case 'ko':
+		return 'KRW';
+	case 'cs':
+		return 'CZK';
+	case 'ru':
+		return 'RUB';
+	case 'pl':
+		return 'PLN';
+	default:
+		return null;
+	}
+}
+
 export function convertTF2PriceToUSD(keys: number, metal: number, keyPrice: number): number {
 	const pureMetal = (keys * keyPrice) + metal;
 
 	// Round price up to nearest cent
   return Math.ceil(pureMetal * conversion_ref_usd * 100) / 100
 }
+
+export function convertUSD(usd: number, currency: string): number {
+	const cur = currency.toUpperCase()
+	if(cur === 'USD') return usd
+
+	throw new Error(`Not implemented`)
+}