Add multilingual language and systems learning tracks

tl/csharp-foundations-20261101/lesson-3/main.cs

@@ -0,0 +1,8 @@
+using System;
+using System.Collections.Generic;
+class Program {
+    static int Remaining(int total, int done) { return done >= total ? 0 : total - done; }
+    static void Main() {
+        Console.WriteLine(Remaining(4, 1));
+    }
+}