diff --git a/astro.config.ts b/astro.config.ts
index 438c0cc51..fcf2a3ae2 100644
--- a/astro.config.ts
+++ b/astro.config.ts
@@ -71,7 +71,7 @@ export default defineConfig({
     remarkPlugins: [remarkMath, remarkGfm],
     rehypePlugins: [
       rehypeSlug,
-      [rehypeMermaid, { strategy: "img-png" }],
+      [rehypeMermaid, { strategy: "pre-mermaid" }],
       [
         rehypeAutolinkHeadings,
         {
diff --git a/src/components/Footer/Subscribe/Subscribe.tsx b/src/components/Footer/Subscribe/Subscribe.tsx
index b3ff1e221..1afdc0e41 100644
--- a/src/components/Footer/Subscribe/Subscribe.tsx
+++ b/src/components/Footer/Subscribe/Subscribe.tsx
@@ -3,7 +3,8 @@ import { useState, useEffect } from "preact/hooks"
 import MailchimpSubscribe from "react-mailchimp-subscribe"
 import SubscribeSvg from "~/assets/svgs/footer/subscribe.svg?react"
 import { clsx } from "~/lib"
-import i18next, { changeLanguage, t } from "i18next"
+import { t } from "i18next"
+import { useI18nReady } from "~/hooks/useI18nReady"
 
 import EmailInput from "./EmailInput.tsx"
 import styles from "./Subscribe.module.css"
@@ -19,8 +20,7 @@ export default function Subscribe(props) {
   const [email, setEmail] = useState("")
   const [customMessage, setCustomMessage] = useState("")
   const [emailValid, setEmailValid] = useState(false)
-
-  i18next.changeLanguage(props.lang)
+  const isReady = useI18nReady(props.lang)
 
   useEffect(() => {
     setCustomMessage("")
@@ -42,6 +42,10 @@ export default function Subscribe(props) {
     setEmail(e.target.value)
   }
 
+  if (!isReady) {
+    return null
+  }
+
   return (
     <div className={clsx(styles.container, "dark:bg-dark-highlight")}>
       <div className={styles.subscribeBox}>
@@ -50,14 +54,20 @@ export default function Subscribe(props) {
         </span>
 
         <div className={styles.copyBox}>
-          <div className={styles.subscribeTitle}>{ t("landing.NewsletterCTA.title") }</div>
-          <div className={styles.subscribeText}>
-          { t("landing.NewsletterCTA.text") }
-          </div>
+          <div className={styles.subscribeTitle}>{t("landing.NewsletterCTA.title")}</div>
+          <div className={styles.subscribeText}>{t("landing.NewsletterCTA.text")}</div>
         </div>
         <MailchimpSubscribe
           url={url}
-          render={({ subscribe, status, message }: any) => (
+          render={({
+            subscribe,
+            status,
+            message,
+          }: {
+            subscribe: (data: { EMAIL: string }) => void
+            status: string
+            message: string
+          }) => (
             <div className={styles.emailBox}>
               <EmailInput
                 className={styles.emailInput}
@@ -65,7 +75,7 @@ export default function Subscribe(props) {
                 onChange={handleChangeEmail}
                 onClick={() => handleSubmit(subscribe)}
                 onEnter={() => handleSubmit(subscribe)}
-                placeholder= { t("landing.NewsletterCTA.placeholder") }
+                placeholder={t("landing.NewsletterCTA.placeholder")}
                 end={status === "success"}
               />
               {customMessage && <div className={styles.errorMessage}>{customMessage}</div>}
diff --git a/src/components/HeadCommon.astro b/src/components/HeadCommon.astro
index f024f2799..934e1914e 100644
--- a/src/components/HeadCommon.astro
+++ b/src/components/HeadCommon.astro
@@ -20,6 +20,12 @@ import "../styles/design-system/global-styles.css"
 <!-- Scrollable a11y code helper -->
 <script src="/make-scrollable-code-focusable.js" is:inline></script>
 
+<!-- Mermaid.js for client-side rendering -->
+<script type="module">
+  import mermaid from "https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs"
+  mermaid.initialize({ startOnLoad: true, theme: "default" })
+</script>
+
 <!-- Google Tag Manager -->
 <!-- <script type="text/javascript">
   ;(function (w, d, s, l, i) {
diff --git a/src/components/RightSidebar/TableOfContents/index.tsx b/src/components/RightSidebar/TableOfContents/index.tsx
index f9e22ea1b..c52b276fd 100644
--- a/src/components/RightSidebar/TableOfContents/index.tsx
+++ b/src/components/RightSidebar/TableOfContents/index.tsx
@@ -3,7 +3,8 @@ import { useStore } from "@nanostores/preact"
 import type { FunctionalComponent } from "preact"
 import { useState, useEffect, useRef } from "preact/hooks"
 import { shouldUpdateToc } from "./tocStore"
-import i18next, { t } from "i18next"
+import { t } from "i18next"
+import { useI18nReady } from "~/hooks/useI18nReady"
 
 export interface Heading {
   depth: number
@@ -21,6 +22,7 @@ const TableOfContents: FunctionalComponent<{
   const [currentID, setCurrentID] = useState("overview")
   const onThisPageID = "on-this-page-heading"
   const $shouldUpdateToc = useStore(shouldUpdateToc)
+  const isReady = useI18nReady()
 
   useEffect(() => {
     if (!tableOfContents.current) return
@@ -79,6 +81,10 @@ const TableOfContents: FunctionalComponent<{
     setHeadings(headingList)
   }
 
+  if (!isReady) {
+    return null
+  }
+
   return (
     <>
       <h2 className="heading">{t("rightSidebar.onThisPage")}</h2>
diff --git a/src/hooks/useI18nReady.ts b/src/hooks/useI18nReady.ts
new file mode 100644
index 000000000..cbbf72860
--- /dev/null
+++ b/src/hooks/useI18nReady.ts
@@ -0,0 +1,69 @@
+import { useState, useEffect } from "preact/hooks"
+import i18next, { changeLanguage } from "i18next"
+
+/**
+ * Custom hook to ensure i18next is initialized and translation resources are loaded
+ * before rendering components that use translations.
+ *
+ * This fixes the issue where Vercel build shows translation keys instead of translated text
+ * due to SSR/CSR timing differences.
+ *
+ * @param lang - Optional language code to change to. If provided, will change language and wait for resources.
+ * @returns boolean indicating if i18next is ready (initialized and resources loaded)
+ */
+export function useI18nReady(lang?: string): boolean {
+  const [isReady, setIsReady] = useState(false)
+
+  useEffect(() => {
+    const ensureResourcesLoaded = async () => {
+      try {
+        // Wait for i18next to be initialized
+        if (!i18next.isInitialized) {
+          await new Promise<void>((resolve) => {
+            const handler = () => {
+              i18next.off("initialized", handler)
+              resolve()
+            }
+            i18next.on("initialized", handler)
+          })
+        }
+
+        // Change language if needed (this will wait for resources to load)
+        if (lang && i18next.language !== lang) {
+          await changeLanguage(lang)
+        }
+
+        // Double-check that resources are actually loaded
+        const targetLang = lang || i18next.language || "en"
+        if (i18next.hasResourceBundle(targetLang, "translation")) {
+          setIsReady(true)
+        } else {
+          // Wait for resources to be loaded
+          await new Promise<void>((resolve) => {
+            const checkResources = () => {
+              if (i18next.hasResourceBundle(targetLang, "translation")) {
+                i18next.off("loaded", checkResources)
+                resolve()
+              }
+            }
+            i18next.on("loaded", checkResources)
+            // Check immediately in case resources are already loaded
+            if (i18next.hasResourceBundle(targetLang, "translation")) {
+              i18next.off("loaded", checkResources)
+              resolve()
+            }
+          })
+          setIsReady(true)
+        }
+      } catch (error) {
+        // If something goes wrong, still set ready to avoid blocking the UI
+        console.error("Error loading i18next resources:", error)
+        setIsReady(true)
+      }
+    }
+
+    ensureResourcesLoaded()
+  }, [lang])
+
+  return isReady
+}
diff --git a/src/styles/index.css b/src/styles/index.css
index 2f33a9317..00b72ba09 100644
--- a/src/styles/index.css
+++ b/src/styles/index.css
@@ -419,3 +419,7 @@ h2.heading {
 .mermaid-diagram > img {
   height: auto;
 }
+
+.mermaid {
+  background: transparent;
+}