diff --git a/imptune/static/app.css b/imptune/static/app.css
index 442c870..5b3cebc 100644
--- a/imptune/static/app.css
+++ b/imptune/static/app.css
@@ -91,6 +91,36 @@ nav.sidebar li {
   border-left-color: var(--pico-primary, #1a73e8);
 }
 
+/* Main wrapper: fills remaining space beside sidebar, stacks topbar + content */
+.main-wrapper {
+  flex: 1 1 auto;
+  min-width: 0;
+  display: flex;
+  flex-direction: column;
+}
+
+/* Topbar: holds top-right controls */
+.topbar {
+  display: flex;
+  justify-content: flex-end;
+  align-items: center;
+  padding: 0.5rem 1rem;
+  border-bottom: 1px solid var(--pico-muted-border-color, #e0e0e0);
+  gap: 0.5rem;
+}
+
+.topbar-controls {
+  display: flex;
+  gap: 0.5rem;
+  align-items: center;
+}
+
+.topbar-controls button {
+  padding: 0.3rem 0.6rem;
+  font-size: 0.85rem;
+  min-width: 2.2rem;
+}
+
 /* Main content */
 .main-content {
   flex: 1 1 auto;
diff --git a/imptune/templates/base.html b/imptune/templates/base.html
index d8d56b9..08c13ea 100644
--- a/imptune/templates/base.html
+++ b/imptune/templates/base.html
@@ -6,6 +6,110 @@
   <title>ImpTune</title>
   <link rel="stylesheet" href="/static/pico.min.css">
   <link rel="stylesheet" href="/static/app.css">
+  <script>
+  document.addEventListener('alpine:init', () => {
+    // Theme store: cycles Light -> Dark -> System, persists in localStorage
+    Alpine.store('theme', {
+      current: localStorage.getItem('imptune_theme') || 'auto',
+      icons: { light: '&#9728;', dark: '&#9790;', auto: '&#9681;' },
+      init() {
+        document.documentElement.setAttribute('data-theme', this.current);
+      },
+      cycle() {
+        const order = ['light', 'dark', 'auto'];
+        this.current = order[(order.indexOf(this.current) + 1) % order.length];
+        localStorage.setItem('imptune_theme', this.current);
+        document.documentElement.setAttribute('data-theme', this.current);
+      }
+    });
+
+    // i18n store: FR/EN toggle, persists in localStorage
+    Alpine.store('i18n', {
+      lang: localStorage.getItem('imptune_lang') || 'fr',
+      t(key) {
+        return (this.translations[this.lang] || {})[key] || key;
+      },
+      toggle() {
+        this.lang = this.lang === 'fr' ? 'en' : 'fr';
+        localStorage.setItem('imptune_lang', this.lang);
+      },
+      translations: {
+        fr: {
+          dashboard: 'Tableau de bord',
+          drivers: 'Pilotes',
+          printers: 'Imprimantes',
+          clients: 'Clients',
+          packages: 'Paquets',
+          add_printer: 'Ajouter une imprimante',
+          add_client: 'Ajouter un client',
+          printer_library: 'Biblioth\u00e8que d\u2019imprimantes',
+          edit: 'Modifier',
+          delete: 'Supprimer',
+          save: 'Enregistrer',
+          cancel: 'Annuler',
+          upload_driver: 'T\u00e9l\u00e9charger un pilote',
+          printer_name: 'Nom de l\u2019imprimante',
+          ip_address: 'Adresse IP',
+          port_name: 'Nom du port',
+          driver: 'Pilote',
+          duplex_mode: 'Mode recto-verso',
+          one_sided: 'Recto simple',
+          long_edge: 'Grand c\u00f4t\u00e9',
+          short_edge: 'Petit c\u00f4t\u00e9',
+          color_mode: 'Mode couleur',
+          paper_size: 'Format papier',
+          collate: 'Assembler',
+          client: 'Client',
+          edit_printer: 'Modifier l\u2019imprimante',
+          no_printers: 'Aucune imprimante configur\u00e9e.',
+          no_clients: 'Aucun client configur\u00e9.',
+          client_list: 'Liste des clients',
+          name: 'Nom',
+          created: 'Cr\u00e9\u00e9 le',
+          back_to_printers: 'Retour aux imprimantes',
+          theme_label: 'Th\u00e8me',
+          lang_label: 'FR'
+        },
+        en: {
+          dashboard: 'Dashboard',
+          drivers: 'Drivers',
+          printers: 'Printers',
+          clients: 'Clients',
+          packages: 'Packages',
+          add_printer: 'Add Printer',
+          add_client: 'Add Client',
+          printer_library: 'Printer Library',
+          edit: 'Edit',
+          delete: 'Delete',
+          save: 'Save',
+          cancel: 'Cancel',
+          upload_driver: 'Upload Driver',
+          printer_name: 'Printer Name',
+          ip_address: 'IP Address',
+          port_name: 'Port Name',
+          driver: 'Driver',
+          duplex_mode: 'Duplex Mode',
+          one_sided: 'One-Sided',
+          long_edge: 'Long Edge',
+          short_edge: 'Short Edge',
+          color_mode: 'Color Mode',
+          paper_size: 'Paper Size',
+          collate: 'Collate',
+          client: 'Client',
+          edit_printer: 'Edit Printer',
+          no_printers: 'No printers configured yet.',
+          no_clients: 'No clients configured yet.',
+          client_list: 'Client List',
+          name: 'Name',
+          created: 'Created',
+          back_to_printers: 'Back to Printers',
+          theme_label: 'Theme',
+          lang_label: 'EN'
+        }
+      }
+    });
+  });
+  </script>
   <script defer src="/static/alpine.min.js"></script>
   <script src="/static/htmx.min.js"></script>
 </head>
@@ -16,16 +120,38 @@
         <strong>ImpTune</strong>
       </div>
       <ul class="sidebar-nav">
-        <li><a href="/" {% if request.url.path == "/" %}class="active"{% endif %}>Dashboard</a></li>
-        <li><a href="/drivers" {% if request.url.path == "/drivers" %}class="active"{% endif %}>Drivers</a></li>
-        <li><a href="/printers" {% if request.url.path == "/printers" %}class="active"{% endif %}>Printers</a></li>
-        <li><a href="/clients" {% if request.url.path == "/clients" %}class="active"{% endif %}>Clients</a></li>
-        <li><a href="/packages" {% if request.url.path == "/packages" %}class="active"{% endif %}>Packages</a></li>
+        <li><a href="/" {% if request.url.path == "/" %}class="active"{% endif %}
+               x-data x-text="$store.i18n.t('dashboard')">Dashboard</a></li>
+        <li><a href="/drivers" {% if request.url.path == "/drivers" %}class="active"{% endif %}
+               x-data x-text="$store.i18n.t('drivers')">Drivers</a></li>
+        <li><a href="/printers" {% if request.url.path == "/printers" %}class="active"{% endif %}
+               x-data x-text="$store.i18n.t('printers')">Printers</a></li>
+        <li><a href="/clients" {% if request.url.path == "/clients" %}class="active"{% endif %}
+               x-data x-text="$store.i18n.t('clients')">Clients</a></li>
+        <li><a href="/packages" {% if request.url.path == "/packages" %}class="active"{% endif %}
+               x-data x-text="$store.i18n.t('packages')">Packages</a></li>
       </ul>
     </nav>
-    <main class="main-content">
-      {% block content %}{% endblock %}
-    </main>
+    <div class="main-wrapper">
+      <header class="topbar">
+        <div class="topbar-controls" x-data>
+          <!-- Theme toggle button: cycles Light -> Dark -> System -->
+          <button class="secondary outline"
+                  x-html="$store.theme.icons[$store.theme.current]"
+                  :aria-label="$store.theme.current"
+                  @click="$store.theme.cycle()"
+                  title="Toggle theme">&#9681;</button>
+          <!-- Language toggle button -->
+          <button class="secondary outline"
+                  x-text="$store.i18n.t('lang_label')"
+                  @click="$store.i18n.toggle()"
+                  title="Toggle language">FR</button>
+        </div>
+      </header>
+      <main class="main-content">
+        {% block content %}{% endblock %}
+      </main>
+    </div>
   </div>
 </body>
 </html>
diff --git a/tests/test_static.py b/tests/test_static.py
index d3fb753..5e22e44 100644
--- a/tests/test_static.py
+++ b/tests/test_static.py
@@ -43,6 +43,16 @@ def test_packages_returns_200(client):
     assert response.status_code == 200
 
 
+
+def test_theme_toggle_present(client):
+    """GET / contains a theme toggle button (data-theme cycling control)."""
+    response = client.get("/")
+    assert response.status_code == 200
+    # The button's @click should reference $store.theme.cycle
+    assert "theme" in response.text
+    assert "cycle" in response.text or "store.theme" in response.text
+
+
 def test_dashboard_shows_recent_printers(client):
     """Dashboard renders names of recently-created printers from DB."""
     from imptune.db.models import Printer
@@ -62,7 +72,17 @@ def test_dashboard_shows_recent_printers(client):
     assert response.status_code == 200
     assert "TestPrinter-Alpha" in response.text
     assert "TestPrinter-Beta" in response.text
-    assert "No printers configured yet" not in response.text
+    # Use class-specific check: the string also appears in the i18n store JS
+    assert 'class="empty-state">No printers configured yet' not in response.text
+
+
+def test_theme_toggle_present(client):
+    """GET / contains a theme toggle button (data-theme cycling control)."""
+    response = client.get("/")
+    assert response.status_code == 200
+    # The button's @click should reference $store.theme.cycle
+    assert "theme" in response.text
+    assert "cycle" in response.text or "store.theme" in response.text
 
 
 def test_dashboard_shows_recent_packages(client):