diff --git a/app/api/profile.py b/app/api/profile.py
index a12324d8..90369f73 100644
--- a/app/api/profile.py
+++ b/app/api/profile.py
@@ -18,7 +18,7 @@ import logging
 from hashlib import md5
 from typing import Annotated
 
-from fastapi import APIRouter, Depends, File, HTTPException, Request, UploadFile, status
+from fastapi import APIRouter, Depends, File, HTTPException, Request, Response, UploadFile, status
 from pydantic import BaseModel, Field
 from sqlalchemy.orm import Session
 
@@ -156,7 +156,9 @@ async def get_profile(request: Request, db: DbSession) -> ProfileResponse:
 
 @router.patch("", response_model=ProfileResponse)
 @require_login
-async def update_profile(body: ProfileUpdateRequest, request: Request, db: DbSession) -> ProfileResponse:
+async def update_profile(
+    body: ProfileUpdateRequest, request: Request, response: Response, db: DbSession
+) -> ProfileResponse:
     """Update the current user's editable profile settings."""
     user_id = _get_user_id(request)
     profile = _get_or_create_profile(db, user_id)
@@ -171,6 +173,24 @@ async def update_profile(body: ProfileUpdateRequest, request: Request, db: DbSes
             )
         profile.preferred_language = lang or None  # type: ignore[assignment]
 
+        # Keep session and cookie in sync so detect_language() picks up
+        # the new preference immediately (without a DB round-trip).
+        if hasattr(request, "session"):
+            if lang:
+                request.session["preferred_language"] = lang
+            else:
+                request.session.pop("preferred_language", None)
+        if lang:
+            response.set_cookie(
+                key="docuelevate_lang",
+                value=lang,
+                max_age=30 * 24 * 60 * 60,
+                httponly=False,
+                samesite="lax",
+            )
+        else:
+            response.delete_cookie(key="docuelevate_lang")
+
     # Validate theme
     if body.preferred_theme is not None:
         theme = body.preferred_theme.lower().strip()
diff --git a/app/views/base.py b/app/views/base.py
index e00f261b..609ff9fb 100644
--- a/app/views/base.py
+++ b/app/views/base.py
@@ -11,7 +11,8 @@ from sqlalchemy.orm import Session  # noqa: F401
 
 from app.auth import require_login  # noqa: F401
 from app.config import settings
-from app.database import get_db  # noqa: F401
+from app.database import SessionLocal, get_db  # noqa: F401
+from app.models import UserProfile
 from app.utils.i18n import (
     SUPPORTED_LANGUAGES,
     detect_language,
@@ -47,6 +48,41 @@ templates.env.globals["_"] = lambda key, **kwargs: translate(key, "en", **kwargs
 original_template_response = templates.TemplateResponse
 
 
+def _hydrate_language_from_db(request: Request, session_user: object) -> None:
+    """Load the user's preferred language from the DB into the session.
+
+    Called once per session when ``preferred_language`` is not yet in the
+    session.  A lightweight DB query fetches the stored preference so that
+    :func:`detect_language` picks it up from the session on all subsequent
+    requests without further DB access.
+    """
+    from app.utils.i18n import SUPPORTED_LANGUAGE_CODES
+
+    user_id: str | None = None
+    if isinstance(session_user, dict):
+        user_id = (
+            session_user.get("sub")
+            or session_user.get("preferred_username")
+            or session_user.get("email")
+            or session_user.get("id")
+        )
+    elif isinstance(session_user, str):
+        user_id = session_user
+
+    if not user_id:
+        return
+
+    db = SessionLocal()
+    try:
+        profile = db.query(UserProfile).filter(UserProfile.user_id == user_id).first()
+        if profile and profile.preferred_language and profile.preferred_language in SUPPORTED_LANGUAGE_CODES:
+            request.session["preferred_language"] = profile.preferred_language
+    except Exception:  # noqa: BLE001 — intentionally broad; DB may be temporarily unavailable
+        logger.debug("Could not hydrate language preference for user_id=%s", user_id)
+    finally:
+        db.close()
+
+
 def _inject_global_context(ctx: dict) -> None:
     """Inject shared global variables into every template context dict."""
     ctx.setdefault("version", settings.version)
@@ -71,6 +107,14 @@ def _inject_global_context(ctx: dict) -> None:
         # When auth is disabled every visitor is effectively "logged in"
         ctx.setdefault("is_logged_in", not getattr(settings, "auth_enabled", True) or session_user is not None)
 
+        # --- Hydrate session language from DB (once per session) ---
+        # If the session doesn't have a preferred_language yet but the user
+        # is logged in, load the stored preference from the database so that
+        # detect_language() picks it up from the session on this and all
+        # subsequent requests.
+        if hasattr(req, "session") and "preferred_language" not in req.session and session_user is not None:
+            _hydrate_language_from_db(req, session_user)
+
         # --- i18n: detect language and register template helpers ---
         current_locale = detect_language(req)
         ctx.setdefault("current_locale", current_locale)
diff --git a/frontend/templates/base.html b/frontend/templates/base.html
index afbe786e..9230423b 100644
--- a/frontend/templates/base.html
+++ b/frontend/templates/base.html
@@ -216,12 +216,18 @@
                     aria-live="polite"></span>
             </a>
 
+            <!-- Language selector data (kept outside the HTML attribute to avoid quote conflicts with tojson) -->
+            <script>
+              window.__langSuggested = {{ suggested_languages | tojson }};
+              window.__langAll = {{ supported_languages | tojson }};
+            </script>
+
             <!-- Language selector dropdown -->
             <div x-data="{
               langOpen: false,
               search: '',
-              suggested: {{ suggested_languages | tojson }},
-              all: {{ supported_languages | tojson }},
+              suggested: window.__langSuggested,
+              all: window.__langAll,
               get filtered() {
                 if (!this.search.trim()) return this.suggested;
                 const q = this.search.trim().toLowerCase();
diff --git a/frontend/templates/profile.html b/frontend/templates/profile.html
index cd506cfb..fc928a80 100644
--- a/frontend/templates/profile.html
+++ b/frontend/templates/profile.html
@@ -327,7 +327,7 @@
 function profileSettings() {
   return {
     // ── State ──────────────────────────────────────────────────────────────
-    avatarUrl: '/static/images/avatar-placeholder.svg',
+    avatarUrl: '/static/images/default-avatar.svg',
     hasCustomAvatar: false,
     isLocalUser: false,
     saving: false,
@@ -349,6 +349,8 @@ function profileSettings() {
     },
 
     // ── Init ───────────────────────────────────────────────────────────────
+    _initialLanguage: '',
+
     async init() {
       try {
         const res = await fetch('/api/profile');
@@ -361,6 +363,7 @@ function profileSettings() {
         this.form.contact_email    = data.contact_email    || '';
         this.form.preferred_language = data.preferred_language || '';
         this.form.preferred_theme    = data.preferred_theme  || 'system';
+        this._initialLanguage = this.form.preferred_language;
       } catch (_e) {
         // Silently ignore — user might not be logged in (rare for this page)
       }
@@ -378,6 +381,7 @@ function profileSettings() {
     async saveProfile() {
       this.saving = true;
       this._hideBanner();
+      const previousLang = this._initialLanguage || '';
       try {
         const csrfToken = this._getCSRFToken();
 
@@ -394,6 +398,11 @@ function profileSettings() {
           this._showBanner(data.detail || 'Failed to save settings.', true);
           return;
         }
+        // If the UI language changed, reload so the page renders in the new locale
+        if (this.form.preferred_language !== previousLang) {
+          window.location.reload();
+          return;
+        }
         this._showBanner('Profile settings saved successfully.', false);
         // Update display name across the nav (refresh the avatar/name)
         if (data.avatar_url) {
diff --git a/tests/test_api_profile.py b/tests/test_api_profile.py
index 65dba9f9..c3391370 100644
--- a/tests/test_api_profile.py
+++ b/tests/test_api_profile.py
@@ -224,9 +224,10 @@ class TestUpdateProfileHandler:
 
         req = MagicMock()
         req.session = {"user": {"preferred_username": "carol", "email": "carol@example.com"}}
+        resp = MagicMock()
 
         body = ProfileUpdateRequest(display_name="Carol Smith")
-        result = await update_profile(body, req, prof_session)
+        result = await update_profile(body, req, resp, prof_session)
         assert result.display_name == "Carol Smith"
 
     @pytest.mark.asyncio
@@ -236,11 +237,31 @@ class TestUpdateProfileHandler:
 
         req = MagicMock()
         req.session = {"user": {"preferred_username": "dave", "email": "dave@example.com"}}
+        resp = MagicMock()
 
         body = ProfileUpdateRequest(preferred_language="de")
-        result = await update_profile(body, req, prof_session)
+        result = await update_profile(body, req, resp, prof_session)
         assert result.preferred_language == "de"
 
+    @pytest.mark.asyncio
+    async def test_updates_language_syncs_session_and_cookie(self, prof_session):
+        """update_profile syncs language to session and cookie."""
+        from app.api.profile import ProfileUpdateRequest, update_profile
+
+        session = {"user": {"preferred_username": "dave2", "email": "dave2@example.com"}}
+        req = MagicMock()
+        req.session = session
+        resp = MagicMock()
+
+        body = ProfileUpdateRequest(preferred_language="fr")
+        await update_profile(body, req, resp, prof_session)
+
+        assert session["preferred_language"] == "fr"
+        resp.set_cookie.assert_called_once()
+        cookie_kwargs = resp.set_cookie.call_args
+        assert cookie_kwargs.kwargs["key"] == "docuelevate_lang"
+        assert cookie_kwargs.kwargs["value"] == "fr"
+
     @pytest.mark.asyncio
     async def test_updates_theme(self, prof_session):
         """update_profile updates preferred_theme."""
@@ -248,9 +269,10 @@ class TestUpdateProfileHandler:
 
         req = MagicMock()
         req.session = {"user": {"preferred_username": "eve", "email": "eve@example.com"}}
+        resp = MagicMock()
 
         body = ProfileUpdateRequest(preferred_theme="light")
-        result = await update_profile(body, req, prof_session)
+        result = await update_profile(body, req, resp, prof_session)
         assert result.preferred_theme == "light"
 
     @pytest.mark.asyncio
@@ -260,10 +282,11 @@ class TestUpdateProfileHandler:
 
         req = MagicMock()
         req.session = {"user": {"preferred_username": "frank", "email": "frank@example.com"}}
+        resp = MagicMock()
 
         body = ProfileUpdateRequest(preferred_language="xx")
         with pytest.raises(HTTPException) as exc:
-            await update_profile(body, req, prof_session)
+            await update_profile(body, req, resp, prof_session)
         assert exc.value.status_code == 422
 
     @pytest.mark.asyncio
@@ -273,13 +296,78 @@ class TestUpdateProfileHandler:
 
         req = MagicMock()
         req.session = {"user": {"preferred_username": "grace", "email": "grace@example.com"}}
+        resp = MagicMock()
 
         body = ProfileUpdateRequest(preferred_theme="rainbow")
         with pytest.raises(HTTPException) as exc:
-            await update_profile(body, req, prof_session)
+            await update_profile(body, req, resp, prof_session)
         assert exc.value.status_code == 422
 
 
+# ---------------------------------------------------------------------------
+# Unit tests — _hydrate_language_from_db (views/base.py)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.unit
+class TestHydrateLanguageFromDb:
+    """Tests for session hydration of preferred_language from DB."""
+
+    def test_hydrates_language_into_session(self, prof_session):
+        """When DB has a preferred_language, it should be set in the session."""
+        from app.views.base import _hydrate_language_from_db
+
+        # Create a profile with a preferred_language
+        profile = UserProfile(user_id="hydrate_user", preferred_language="fr")
+        prof_session.add(profile)
+        prof_session.commit()
+
+        req = MagicMock()
+        req.session = {}
+        session_user = {"preferred_username": "hydrate_user"}
+
+        # Patch SessionLocal to return our test session
+        from unittest.mock import patch
+
+        with patch("app.views.base.SessionLocal", return_value=prof_session):
+            _hydrate_language_from_db(req, session_user)
+
+        assert req.session.get("preferred_language") == "fr"
+
+    def test_no_hydration_when_no_db_preference(self, prof_session):
+        """When DB has no preferred_language, session should remain empty."""
+        from app.views.base import _hydrate_language_from_db
+
+        profile = UserProfile(user_id="no_pref_user")
+        prof_session.add(profile)
+        prof_session.commit()
+
+        req = MagicMock()
+        req.session = {}
+        session_user = {"preferred_username": "no_pref_user"}
+
+        from unittest.mock import patch
+
+        with patch("app.views.base.SessionLocal", return_value=prof_session):
+            _hydrate_language_from_db(req, session_user)
+
+        assert "preferred_language" not in req.session
+
+    def test_no_hydration_when_no_user_id(self, prof_session):
+        """When session_user has no identifiable user_id, do nothing."""
+        from app.views.base import _hydrate_language_from_db
+
+        req = MagicMock()
+        req.session = {}
+
+        from unittest.mock import patch
+
+        with patch("app.views.base.SessionLocal", return_value=prof_session):
+            _hydrate_language_from_db(req, {})
+
+        assert "preferred_language" not in req.session
+
+
 # ---------------------------------------------------------------------------
 # Unit tests — POST /api/profile/avatar handler
 # ---------------------------------------------------------------------------