diff --git a/environment.yml b/environment.yml
index bb972015..3af743aa 100644
--- a/environment.yml
+++ b/environment.yml
@@ -7,7 +7,7 @@ dependencies:
   - pip
   - pip:
     - jupyter-book>=1.0.4post1,<2.0
-    - quantecon-book-theme==0.19.0
+    - quantecon-book-theme==0.20.0
     - sphinx-tojupyter==0.6.0
     - sphinxext-rediraffe==0.3.0
     - sphinx-exercise==1.2.1
diff --git a/lectures/_config.yml b/lectures/_config.yml
index c3fe4825..0183ce65 100644
--- a/lectures/_config.yml
+++ b/lectures/_config.yml
@@ -35,6 +35,17 @@ sphinx:
     html_theme: quantecon_book_theme
     html_static_path: ['_static']
     html_theme_options:
+      languages:
+        - code: en
+          name: English
+          url: https://python-programming.quantecon.org
+        - code: fa
+          name: فارسی
+          url: https://quantecon.github.io/lecture-python-programming.fa
+        - code: zh-cn
+          name: 中文
+          url: https://quantecon.github.io/lecture-python-programming.zh-cn
+      current_language: en
       authors:
         - name: Thomas J. Sargent
           url: http://www.tomsargent.com/