diff --git a/src/app/forum/page.tsx b/src/app/forum/page.tsx
index 7e65218..9f0ccbd 100644
--- a/src/app/forum/page.tsx
+++ b/src/app/forum/page.tsx
@@ -4,6 +4,7 @@ import Link from 'next/link';
 import Header from '@/components/Header';
 import Footer from '@/components/Footer';
 import AdImage from '@/components/AdImage';
+import SidebarAdStack from '@/components/SidebarAdStack';
 import { ADS_728X90, shuffle } from '@/lib/ads';
 import { createClient } from '@/lib/supabase/client';
 
@@ -274,6 +275,8 @@ export default function ForumIndexPage() {
         </div>
 
         <div className="max-w-container mx-auto px-4 py-6">
+          <div className="lg:grid lg:grid-cols-[1fr,300px] lg:gap-8">
+          <div>
 
           {/* Feed Mode Tabs */}
           <div className="flex items-center gap-1 bg-[#1a1a1a] border border-[#2a2a2a] rounded-lg p-1 mb-6 w-fit">
@@ -576,6 +579,15 @@ export default function ForumIndexPage() {
               <AdImage ad={shuffle(ADS_728X90)[0]} page="forum" />
             </div>
           )}
+
+          </div>
+          {/* Sidebar: 300x600 + every rotating 300x250 */}
+          <aside className="mt-10 lg:mt-0" aria-label="Advertisements">
+            <div className="lg:sticky lg:top-24">
+              <SidebarAdStack />
+            </div>
+          </aside>
+          </div>
         </div>
       </main>
       <Footer />
diff --git a/src/app/forum/thread/[id]/page.tsx b/src/app/forum/thread/[id]/page.tsx
index 5126f65..0316ab2 100644
--- a/src/app/forum/thread/[id]/page.tsx
+++ b/src/app/forum/thread/[id]/page.tsx
@@ -4,8 +4,23 @@ import Link from 'next/link';
 import { useParams } from 'next/navigation';
 import Header from '@/components/Header';
 import Footer from '@/components/Footer';
+import AdImage from '@/components/AdImage';
+import { ADS_300X250, rotateAll } from '@/lib/ads';
 import { createClient } from '@/lib/supabase/client';
 
+// Inline ad slot inserted between forum replies every N posts.
+function InThreadAd({ adIndex }: { adIndex: number }) {
+  const pool = ADS_300X250;
+  if (pool.length === 0) return null;
+  const ad = pool[adIndex % pool.length];
+  return (
+    <div className="bg-[#0d1117] border border-dashed border-[#2a3a50] rounded-lg p-4 my-3 flex flex-col items-center gap-2" aria-label="Advertisement">
+      <span className="text-[10px] font-mono uppercase tracking-[0.18em] text-[#6b7280]">Sponsored</span>
+      <AdImage ad={ad} page="forum-thread" />
+    </div>
+  );
+}
+
 interface ForumThread {
   id: string;
   title: string;
@@ -362,42 +377,48 @@ export default function ForumThreadPage() {
             {replies.length > 0 && (
               <div className="space-y-3 mb-6">
                 {replies.map((reply, idx) => (
-                  <div
-                    key={reply.id}
-                    className={`border rounded-lg p-5 ${
-                      reply.is_ai_response
-                        ? 'bg-[#0d1f35] border-[#1e3a5f]'
-                        : 'bg-[#1a1a1a] border-[#252525]'
-                    }`}
-                  >
-                    <div className="flex items-start gap-3">
-                      <Avatar name={reply.author_name} isAI={reply.is_ai_response} />
-                      <div className="flex-1 min-w-0">
-                        <div className="flex items-center gap-2 mb-2 flex-wrap">
-                          <span className="text-white font-body font-semibold text-sm">{reply.author_name}</span>
-                          {reply.is_ai_response && (
-                            <span className="text-xs bg-[#3b82f6]/20 text-[#3b82f6] border border-[#3b82f6]/30 px-2 py-0.5 rounded font-body font-semibold">
-                              AI Assistant
-                            </span>
-                          )}
-                          <span className="text-[#555] font-body text-xs">·</span>
-                          <span className="text-[#555] font-body text-xs">#{idx + 1}</span>
-                          <span className="text-[#555] font-body text-xs">·</span>
-                          <span className="text-[#555] font-body text-xs">{timeAgo(reply.created_at)}</span>
+                  <React.Fragment key={reply.id}>
+                    <div
+                      className={`border rounded-lg p-5 ${
+                        reply.is_ai_response
+                          ? 'bg-[#0d1f35] border-[#1e3a5f]'
+                          : 'bg-[#1a1a1a] border-[#252525]'
+                      }`}
+                    >
+                      <div className="flex items-start gap-3">
+                        <Avatar name={reply.author_name} isAI={reply.is_ai_response} />
+                        <div className="flex-1 min-w-0">
+                          <div className="flex items-center gap-2 mb-2 flex-wrap">
+                            <span className="text-white font-body font-semibold text-sm">{reply.author_name}</span>
+                            {reply.is_ai_response && (
+                              <span className="text-xs bg-[#3b82f6]/20 text-[#3b82f6] border border-[#3b82f6]/30 px-2 py-0.5 rounded font-body font-semibold">
+                                AI Assistant
+                              </span>
+                            )}
+                            <span className="text-[#555] font-body text-xs">·</span>
+                            <span className="text-[#555] font-body text-xs">#{idx + 1}</span>
+                            <span className="text-[#555] font-body text-xs">·</span>
+                            <span className="text-[#555] font-body text-xs">{timeAgo(reply.created_at)}</span>
+                          </div>
+                          <p className="text-[#d0d0d0] font-body text-sm leading-relaxed whitespace-pre-wrap">{reply.body}</p>
+                          <VoteButtons
+                            targetType="reply"
+                            targetId={reply.id}
+                            upvotes={reply.upvotes ?? 0}
+                            downvotes={reply.downvotes ?? 0}
+                            voteScore={reply.vote_score ?? 0}
+                            isAI={reply.is_ai_response}
+                            isAuthenticated={isAuthenticated}
+                          />
                         </div>
-                        <p className="text-[#d0d0d0] font-body text-sm leading-relaxed whitespace-pre-wrap">{reply.body}</p>
-                        <VoteButtons
-                          targetType="reply"
-                          targetId={reply.id}
-                          upvotes={reply.upvotes ?? 0}
-                          downvotes={reply.downvotes ?? 0}
-                          voteScore={reply.vote_score ?? 0}
-                          isAI={reply.is_ai_response}
-                          isAuthenticated={isAuthenticated}
-                        />
                       </div>
                     </div>
-                  </div>
+                    {/* In-thread 300x250 ad after every 4 replies (idx 3, 7, 11, …),
+                        unless it's the last reply (avoid trailing ad). */}
+                    {(idx + 1) % 4 === 0 && idx < replies.length - 1 && (
+                      <InThreadAd adIndex={Math.floor(idx / 4)} />
+                    )}
+                  </React.Fragment>
                 ))}
                 <div ref={repliesEndRef} />
               </div>
diff --git a/src/app/newsletter/archive/page.tsx b/src/app/newsletter/archive/page.tsx
index 8ea4320..1e68bf3 100644
--- a/src/app/newsletter/archive/page.tsx
+++ b/src/app/newsletter/archive/page.tsx
@@ -4,6 +4,7 @@ import React, { useState, useEffect, useCallback, useId } from "react";
 import Link from "next/link";
 import Header from "@/components/Header";
 import Footer from "@/components/Footer";
+import SidebarAdStack from "@/components/SidebarAdStack";
 
 // ─── Types ────────────────────────────────────────────────────────────────────
 interface ArticleBlock {
@@ -538,6 +539,9 @@ export default function NewsletterArchivePage() {
 
           {/* ── Right: Sidebar ─────────────────────────────────────────────── */}
           <aside className="lg:col-span-4 space-y-6">
+            {/* 300x600 + rotating 300x250 stack */}
+            <SidebarAdStack />
+
             {/* Signup CTA */}
             <SignupCTA />
 
diff --git a/src/components/LanguageSwitcher.tsx b/src/components/LanguageSwitcher.tsx
index f9bba31..4589e2b 100644
--- a/src/components/LanguageSwitcher.tsx
+++ b/src/components/LanguageSwitcher.tsx
@@ -31,11 +31,52 @@ function setLangCookie(lang: LangCode) {
 }
 
 // ─── Browser language detection ──────────────────────────────────────────────
+// Strategy (in order):
+//   1. If the user's timezone is in an English-speaking region (US/CA/UK/AU/NZ),
+//      always return 'en'. This avoids the case where a US user has an OS
+//      locale of pt-BR or es-MX accidentally set but is clearly browsing
+//      from the US.
+//   2. Otherwise walk navigator.languages (the full preference list) and
+//      return the first base code we support.
+//   3. Fallback to 'en'.
 function detectBrowserLang(): LangCode {
   if (typeof navigator === 'undefined') return 'en';
-  const browserLang = navigator.language?.toLowerCase().split('-')[0] || 'en';
-  const supported = SUPPORTED_LANGUAGES.map(l => l.code);
-  return (supported.includes(browserLang as LangCode) ? browserLang : 'en') as LangCode;
+
+  const supported = new Set(SUPPORTED_LANGUAGES.map(l => l.code as string));
+
+  // 1. Timezone → English-region override
+  try {
+    const tz = Intl.DateTimeFormat().resolvedOptions().timeZone || '';
+    const englishRegions = [
+      'America/',          // US, Canada, most of Latin America (we still bias en here — see note)
+      'Pacific/Honolulu',
+      'Pacific/Auckland', 'Pacific/Wellington',
+      'Australia/',
+      'Europe/London', 'Europe/Dublin',
+      'Atlantic/Reykjavik',
+    ];
+    // For America/* we want en specifically for US/CA/etc. Latin America also
+    // matches America/* — but English is widely understood and we don't have
+    // localized content; better to default to en and let the user opt into
+    // another language via the pulldown.
+    if (englishRegions.some(prefix => tz === prefix || tz.startsWith(prefix))) {
+      return 'en';
+    }
+  } catch {
+    // Intl unavailable — fall through
+  }
+
+  // 2. Walk navigator.languages and pick first supported
+  const langList: string[] = Array.isArray(navigator.languages) && navigator.languages.length > 0
+    ? Array.from(navigator.languages)
+    : (navigator.language ? [navigator.language] : ['en']);
+
+  for (const raw of langList) {
+    const base = raw.toLowerCase().split('-')[0];
+    if (supported.has(base)) return base as LangCode;
+  }
+
+  return 'en';
 }
 
 // ─── Language Switcher Component ─────────────────────────────────────────────