Restructured the project structure back to the way it was, there's no reasonable way to split the modules

src/NadekoBot/_common/ICurrencyProvider.cs

@@ -0,0 +1,29 @@
+using System.Globalization;
+using System.Numerics;
+
+namespace NadekoBot.Common;
+
+public interface ICurrencyProvider
+{
+    string GetCurrencySign();
+}
+
+public static class CurrencyHelper
+{
+    public static string N<T>(T cur, IFormatProvider format)
+        where T : INumber<T>
+        => cur.ToString("C0", format);
+
+    public static string N<T>(T cur, CultureInfo culture, string currencySign)
+        where T : INumber<T>
+        => N(cur, GetCurrencyFormat(culture, currencySign));
+
+    private static IFormatProvider GetCurrencyFormat(CultureInfo culture, string currencySign)
+    {
+        var flowersCurrencyCulture = (CultureInfo)culture.Clone();
+        flowersCurrencyCulture.NumberFormat.CurrencySymbol = currencySign;
+        flowersCurrencyCulture.NumberFormat.CurrencyNegativePattern = 5;
+
+        return flowersCurrencyCulture;
+    }
+}