diff --git a/app/routers/universe.py b/app/routers/universe.py
index d8d64ee..ea1d633 100644
--- a/app/routers/universe.py
+++ b/app/routers/universe.py
@@ -362,10 +362,19 @@ async def analyze_portfolio(
     except Exception:
         raise HTTPException(status_code=400, detail="malformed JSON body")
 
-    user_lang = (
+    # Resolve lang. The frontend sends the live toggle state in
+    # payload["lang"]; that's what the user is *looking at* right now
+    # and is the most up-to-date value. user.lang from the DB is the
+    # persisted preference and is used as a fallback when the frontend
+    # didn't send anything (older clients, scripts, direct curl).
+    db_lang = (
         principal.user.lang if (principal.user and principal.user.lang) else "en"
     )
-    payload["lang"] = user_lang
+    incoming = (payload.get("lang") or "").strip().lower()
+    payload["lang"] = incoming or db_lang
+    log.info("analyze.lang_resolved",
+             payload_lang=incoming or None, db_lang=db_lang,
+             final=payload["lang"])
 
     try:
         req = portfolio_analysis.parse_request(payload)
diff --git a/app/static/js/portfolio.js b/app/static/js/portfolio.js
index 767f078..7ab75f5 100644
--- a/app/static/js/portfolio.js
+++ b/app/static/js/portfolio.js
@@ -469,6 +469,13 @@
       }
     }
 
+    // The language toggle's data-lang attribute is the user's LIVE
+    // pick — newer than user.lang in the DB if the user toggled and
+    // hit Generate/Regenerate before the toggle-PATCH committed.
+    // Backend prefers this value if provided (see universe.py).
+    const langPill = document.getElementById('lang-toggle');
+    const userLang = (langPill && langPill.dataset.lang) || 'en';
+
     try {
       const r = await fetch('/api/analyze', {
         method: 'POST',
@@ -478,6 +485,7 @@
           positions: pie.positions,
           prices: prices,
           base_currency: pie.base_currency || 'GBP',
+          lang: userLang,
         }),
       });
       const data = await r.json();