diff --git a/.github/workflows/rbe.yml b/.github/workflows/rbe.yml
index c24ec76737..03bbe08829 100644
--- a/.github/workflows/rbe.yml
+++ b/.github/workflows/rbe.yml
@@ -4,6 +4,7 @@ on: [push, pull_request]
 env:
   # Update the language picker in index.hbs to link new languages.
   LANGUAGES: ja zh es
+  MDBOOK_VERSION: 0.5.1
 
 jobs:
   test:
@@ -27,12 +28,12 @@ jobs:
     - name: Install mdbook
       run: |
         mkdir bin
-        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v0.4.51/mdbook-v0.4.51-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
+        curl -sSL https://github.com/rust-lang/mdBook/releases/download/v${MDBOOK_VERSION}/mdbook-v${MDBOOK_VERSION}-x86_64-unknown-linux-gnu.tar.gz | tar -xz --directory=bin
         echo "$(pwd)/bin" >> ${GITHUB_PATH}
 
     - name: Install mdbook-i18n-helpers
       run: |
-        cargo install mdbook-i18n-helpers --locked --version 0.3.4
+        cargo install mdbook-i18n-helpers --locked --version 0.4.0
 
     - name: Report versions
       run: |
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 21c4d4567b..ffc8be1fe5 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -56,8 +56,7 @@ $ mdbook build
 **The following warnings can be ignored safely.**
 
 ```text
-[WARN] (mdbook::preprocess::cmd): The command wasn't found, is the "gettext" preprocessor installed?
-[WARN] (mdbook::preprocess::cmd):   Command: mdbook-gettext
+ WARN The command `mdbook-gettext` for preprocessor `gettext` was not found, but is marked as optional.
 ```
 
 [install Rust]: http://rust-lang.org/install.html
diff --git a/README.md b/README.md
index b7a7dbf879..d56a73aeba 100644
--- a/README.md
+++ b/README.md
@@ -27,8 +27,7 @@ read all content offline, however!
 **The following warnings can be ignored safely.**
 
 ```text
-[WARN] (mdbook::preprocess::cmd): The command wasn't found, is the "gettext" preprocessor installed?
-[WARN] (mdbook::preprocess::cmd):   Command: mdbook-gettext
+ WARN The command `mdbook-gettext` for preprocessor `gettext` was not found, but is marked as optional.
 ```
 
 ### Using translated version
diff --git a/book.toml b/book.toml
index 65d8616b18..fc8ba714b1 100644
--- a/book.toml
+++ b/book.toml
@@ -17,7 +17,6 @@ hash-files = true
 additional-css = [
   "theme/css/language-picker.css",
 ]
-additional-js = ["theme/js/language-picker.js"]
 
 [rust]
 edition = "2021"
diff --git a/theme/head.hbs b/theme/head.hbs
index f9a6286907..9cbd85dfbf 100644
--- a/theme/head.hbs
+++ b/theme/head.hbs
@@ -1,4 +1,71 @@
 <script>
-    const mdbookPath = "{{ path }}";
-    const mdbookPathToRoot = "{{ path_to_root }}";
+    document.addEventListener('DOMContentLoaded', function() {
+        const mdbookPath = "{{ path }}";
+        const mdbookPathToRoot = "{{ path_to_root }}";
+        const rightButtonsElement = document.querySelector('.right-buttons');
+        rightButtonsElement.insertAdjacentHTML("afterbegin", `
+            <button id="language-toggle" class="icon-button" type="button"
+                    title="Change language" aria-label="Change language"
+                    aria-haspopup="true" aria-expanded="false"
+                    aria-controls="language-list">
+                {{fa "solid" "globe"}}
+            </button>
+            <ul id="language-list" class="theme-popup" aria-label="Languages" role="menu">
+              <li role="none"><button role="menuitem" class="theme">
+                  <a id="en">English</a>
+              </button></li>
+              <li role="none"><button role="menuitem" class="theme">
+                  <a id="ja">日本語</a>
+              </button></li>
+              <li role="none"><button role="menuitem" class="theme">
+                  <a id="zh">中文</a>
+              </button></li>
+              <li role="none"><button role="menuitem" class="theme">
+                  <a id="es">Español</a>
+              </button></li>
+            </ul>
+        `);
+
+        const language = document.documentElement.getAttribute("lang");
+        let langToggle = document.getElementById("language-toggle");
+        let langList = document.getElementById("language-list");
+        langToggle.addEventListener("click", (event) => {
+            langList.style.display =
+                langList.style.display == "block" ? "none" : "block";
+        });
+        let selectedLang = document.getElementById(language);
+        if (selectedLang) {
+            selectedLang.parentNode.classList.add("theme-selected");
+        }
+
+        // The path to the root, taking the current language into account.
+        let full_path_to_root =
+            language == "en" ? `${mdbookPathToRoot}` : `${mdbookPathToRoot}../`;
+        // The page path (mdbook only gives us access to the path to the Markdown file).
+        let path = mdbookPath.replace(/\.md$/, ".html");
+        const langAnchors = Array.from(langList.querySelectorAll("a"));
+        for (let lang of langAnchors) {
+            if (lang.id == "en") {
+                lang.href = `${full_path_to_root}${path}`;
+            } else {
+                lang.href = `${full_path_to_root}${lang.id}/${path}`;
+            }
+        }
+
+        // Hide languages whose target page is not available (e.g., not deployed).
+        // This prevents users from hitting 404s on sites that only ship some locales.
+        for (let lang of langAnchors) {
+            const url = lang.href;
+            // Attempt a lightweight HEAD request; fall back to hiding on failure.
+            fetch(url, { method: "HEAD" }).then((resp) => {
+                if (!resp.ok) {
+                    const li = lang.parentNode && lang.parentNode.parentNode;
+                    if (li) li.style.display = "none";
+                }
+            }).catch(() => {
+                const li = lang.parentNode && lang.parentNode.parentNode;
+                if (li) li.style.display = "none";
+            });
+        }
+    });
 </script>
diff --git a/theme/js/language-picker.js b/theme/js/language-picker.js
deleted file mode 100644
index 02d8d18d9e..0000000000
--- a/theme/js/language-picker.js
+++ /dev/null
@@ -1,67 +0,0 @@
-(function addThemePicker() {
-    const rightButtonsElement = document.querySelector('.right-buttons');
-    rightButtonsElement.insertAdjacentHTML("afterbegin", `
-        <button id="language-toggle" class="icon-button" type="button"
-                title="Change language" aria-label="Change language"
-                aria-haspopup="true" aria-expanded="false"
-                aria-controls="language-list">
-            <i class="fa fa-globe"></i>
-        </button>
-        <ul id="language-list" class="theme-popup" aria-label="Languages" role="menu">
-          <li role="none"><button role="menuitem" class="theme">
-              <a id="en">English</a>
-          </button></li>
-          <li role="none"><button role="menuitem" class="theme">
-              <a id="ja">日本語</a>
-          </button></li>
-          <li role="none"><button role="menuitem" class="theme">
-              <a id="zh">中文</a>
-          </button></li>
-          <li role="none"><button role="menuitem" class="theme">
-              <a id="es">Español</a>
-          </button></li>
-        </ul>
-    `);
-
-    const language = document.documentElement.getAttribute("lang");
-    let langToggle = document.getElementById("language-toggle");
-    let langList = document.getElementById("language-list");
-    langToggle.addEventListener("click", (event) => {
-        langList.style.display =
-            langList.style.display == "block" ? "none" : "block";
-    });
-    let selectedLang = document.getElementById(language);
-    if (selectedLang) {
-        selectedLang.parentNode.classList.add("theme-selected");
-    }
-
-    // The path to the root, taking the current language into account.
-    let full_path_to_root =
-        language == "en" ? `${mdbookPathToRoot}` : `${mdbookPathToRoot}../`;
-    // The page path (mdbook only gives us access to the path to the Markdown file).
-    let path = mdbookPath.replace(/\.md$/, ".html");
-    const langAnchors = Array.from(langList.querySelectorAll("a"));
-    for (let lang of langAnchors) {
-        if (lang.id == "en") {
-            lang.href = `${full_path_to_root}${path}`;
-        } else {
-            lang.href = `${full_path_to_root}${lang.id}/${path}`;
-        }
-    }
-
-    // Hide languages whose target page is not available (e.g., not deployed).
-    // This prevents users from hitting 404s on sites that only ship some locales.
-    for (let lang of langAnchors) {
-        const url = lang.href;
-        // Attempt a lightweight HEAD request; fall back to hiding on failure.
-        fetch(url, { method: "HEAD" }).then((resp) => {
-            if (!resp.ok) {
-                const li = lang.parentNode && lang.parentNode.parentNode;
-                if (li) li.style.display = "none";
-            }
-        }).catch(() => {
-            const li = lang.parentNode && lang.parentNode.parentNode;
-            if (li) li.style.display = "none";
-        });
-    }
-})();