Retranslate the complete English edition from Simplified Chinese (#2010)

* Retranslate the complete English edition from Simplified Chinese

* Polish three English explanations after reader-focused review

en/codes/java/chapter_tree/binary_tree_bfs.java

@@ -12,31 +12,31 @@ import java.util.*;
 public class binary_tree_bfs {
     /* Level-order traversal */
     static List<Integer> levelOrder(TreeNode root) {
-        // Initialize queue, add root node
+        // Initialize a queue and enqueue the root
         Queue<TreeNode> queue = new LinkedList<>();
         queue.add(root);
-        // Initialize a list to save the traversal sequence
+        // Initialize a list to store the traversal sequence
         List<Integer> list = new ArrayList<>();
         while (!queue.isEmpty()) {
-            TreeNode node = queue.poll(); // Dequeue
-            list.add(node.val);           // Save node value
+            TreeNode node = queue.poll(); // Dequeue from the queue
+            list.add(node.val);           // Store the node value
             if (node.left != null)
-                queue.offer(node.left);   // Left child node enqueue
+                queue.offer(node.left);   // Enqueue the left child
             if (node.right != null)
-                queue.offer(node.right);  // Right child node enqueue
+                queue.offer(node.right);  // Enqueue the right child
         }
         return list;
     }
 
     public static void main(String[] args) {
-        /* Initialize binary tree */
-        // Here we use a function to generate a binary tree directly from an array
+        /* Initialize the binary tree */
+        // Use a helper function that builds a binary tree directly from an array
         TreeNode root = TreeNode.listToTree(Arrays.asList(1, 2, 3, 4, 5, 6, 7));
-        System.out.println("\nInitialize binary tree\n");
+        System.out.println("\nInitialize the binary tree\n");
         PrintUtil.printTree(root);
 
         /* Level-order traversal */
         List<Integer> list = levelOrder(root);
-        System.out.println("\nLevel-order traversal node print sequence = " + list);
+        System.out.println("\nNode sequence from level-order traversal = " + list);
     }
 }