docs: add Japanese translate documents (#1812)

* docs: add Japanese documents (`ja/docs`)

* docs: add Japanese documents (`ja/codes`)

* docs: add Japanese documents

* Remove pythontutor blocks in ja/

* Add an empty at the end of each markdown file.

* Add the missing figures (use the English version temporarily).

* Add index.md for Japanese version.

* Add index.html for Japanese version.

* Add missing index.assets

* Fix backtracking_algorithm.md for Japanese version.

* Add avatar_eltociear.jpg. Fix image links on the Japanese landing page.

* Add the Japanese banner.

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Co-authored-by: krahets <krahets@163.com>

ja/codes/java/chapter_dynamic_programming/climbing_stairs_dfs.java

@@ -0,0 +1,31 @@
+/**
+ * File: climbing_stairs_dfs.java
+ * Created Time: 2023-06-30
+ * Author: krahets (krahets@163.com)
+ */
+
+package chapter_dynamic_programming;
+
+public class climbing_stairs_dfs {
+    /* 探索 */
+    public static int dfs(int i) {
+        // 既知の dp[1] と dp[2] を返す
+        if (i == 1 || i == 2)
+            return i;
+        // dp[i] = dp[i-1] + dp[i-2]
+        int count = dfs(i - 1) + dfs(i - 2);
+        return count;
+    }
+
+    /* 階段登り：探索 */
+    public static int climbingStairsDFS(int n) {
+        return dfs(n);
+    }
+
+    public static void main(String[] args) {
+        int n = 9;
+
+        int res = climbingStairsDFS(n);
+        System.out.println(String.format("%d段の階段を登る解は%d通りです", n, res));
+    }
+}