diff --git a/app/routers/chat.py b/app/routers/chat.py
index 20f99e5..6e12a8e 100644
--- a/app/routers/chat.py
+++ b/app/routers/chat.py
@@ -21,7 +21,7 @@ from app.db import get_session, utcnow
 from app.jobs._market_context import REFERENCE_LINE
 from app.models import AICall, Headline, Quote, StrategicLog
 from app.routers.api import _md_to_html
-from app.services.i18n import respond_in_clause
+from app.services.i18n import language_directive_lead, respond_in_clause
 from app.services.llm_prompts import build_chat_system_prompt
 from app.services.openrouter import call_llm, month_start
 from app.services.output_review import review_read
@@ -165,13 +165,17 @@ async def chat(
         headlines=headlines,
         reference_line=REFERENCE_LINE,
     )
-    # Respect the user's interface language preference: append a single
-    # localized "respond in" nudge so the assistant answers in IT when
-    # the user has lang=it. The prompt + history (which includes the
-    # user's own question, often in their language) are usually enough,
-    # but the nudge guarantees the first reply lands correctly.
+    # Respect the user's interface language preference. The tail
+    # "Respond in X" clause is easy for the model to drop when the
+    # rest of the prompt is English (long log content, English
+    # market data, English headlines), so we ALSO prepend a stronger
+    # language directive at the top — see services/i18n.
     user_lang = principal.user.lang if principal and principal.user else "en"
-    system_prompt = system_prompt + respond_in_clause(user_lang)
+    system_prompt = (
+        language_directive_lead(user_lang)
+        + system_prompt
+        + respond_in_clause(user_lang)
+    )
 
     msgs = [{"role": "system", "content": system_prompt}]
     for m in history:
diff --git a/app/services/i18n.py b/app/services/i18n.py
index 742373d..55d00da 100644
--- a/app/services/i18n.py
+++ b/app/services/i18n.py
@@ -46,3 +46,31 @@ def respond_in_clause(lang: str | None) -> str:
     if not lang or lang == "en" or lang not in LANGUAGES:
         return ""
     return f"\n\nRespond in {LANGUAGES[lang]}."
+
+
+def language_directive_lead(lang: str | None) -> str:
+    """Strong, top-of-prompt language directive for callers that
+    generate user-facing prose in real time (portfolio analysis,
+    chat) and need the output to actually land in the user's
+    preferred language. A single tail clause like
+    ``respond_in_clause`` is easy for the model to ignore when the
+    rest of the prompt + user message are entirely in English; this
+    leads with an explicit "all output in X" block, kept verbatim
+    rules for symbols/numbers, and is intended to be prepended to
+    the system prompt so the model anchors on the target language
+    before reading the rest. Combined with respond_in_clause at the
+    tail it gives a belt-and-suspenders defence.
+
+    Empty string for English or unknown codes so callers can paste
+    it in unconditionally.
+    """
+    if not lang or lang == "en" or lang not in LANGUAGES:
+        return ""
+    language = LANGUAGES[lang]
+    return (
+        f"# LANGUAGE — write everything in {language}\n"
+        f"All output — section headers, prose, lists, and any inline "
+        f"labels — must be written in {language}. Do NOT mix English in. "
+        f"Ticker symbols (AAPL, MSFT, VOD.L), ISO currency codes "
+        f"(USD, EUR, GBP), and numeric values stay unchanged.\n\n"
+    )
diff --git a/app/services/portfolio_analysis.py b/app/services/portfolio_analysis.py
index 1f6bea7..dfd3cb1 100644
--- a/app/services/portfolio_analysis.py
+++ b/app/services/portfolio_analysis.py
@@ -31,7 +31,7 @@ from app.config import get_settings
 from app.db import utcnow
 from app.logging import get_logger
 from app.models import AICall
-from app.services.i18n import LANGUAGES, respond_in_clause
+from app.services.i18n import LANGUAGES, language_directive_lead, respond_in_clause
 from app.services.llm_prompts import build_system_prompt
 from app.services.output_review import review_read
 from app.services.openrouter import (
@@ -282,7 +282,18 @@ def build_prompt(req: AnalysisRequest) -> tuple[str, str]:
     head = enriched[:MAX_POSITIONS_INLINED]
     tail_count = max(0, len(enriched) - MAX_POSITIONS_INLINED)
 
-    system = build_system_prompt(req.tone, req.analysis) + "\n\n" + _SYSTEM_OVERRIDES + respond_in_clause(req.lang)
+    # Language directive both prepended (so the model anchors on the
+    # target language before reading the long English instruction
+    # block) and appended (defence in depth — a tail nudge alone
+    # was being ignored by deepseek-v4-flash when most of the
+    # context is English).
+    system = (
+        language_directive_lead(req.lang)
+        + build_system_prompt(req.tone, req.analysis)
+        + "\n\n"
+        + _SYSTEM_OVERRIDES
+        + respond_in_clause(req.lang)
+    )
 
     user_parts = [
         f"# Portfolio commentary request — {utcnow().strftime('%Y-%m-%d')}",