diff --git a/tests/e2e/test_i18n_toggle.py b/tests/e2e/test_i18n_toggle.py
new file mode 100644
index 0000000..ff19f49
--- /dev/null
+++ b/tests/e2e/test_i18n_toggle.py
@@ -0,0 +1,59 @@
+"""UIE-05: E2E tests for language toggle — FR/EN switching and localStorage persistence."""
+from __future__ import annotations
+import pytest
+
+
+def test_language_toggle_switches_nav_label(page, live_server: str) -> None:
+    """Clicking FR/EN button switches nav label from French to English."""
+    page.goto(f"{live_server}/", wait_until="domcontentloaded")
+
+    # Default lang is 'fr' — nav should show French labels
+    # Wait for Alpine to hydrate
+    page.wait_for_function(
+        "document.querySelector('nav a[href=\"/printers\"]').textContent.trim() !== ''",
+        timeout=3000,
+    )
+
+    # In French, printers nav label = 'Imprimantes'
+    printers_label_fr = page.text_content("nav a[href='/printers']").strip()
+    assert printers_label_fr == "Imprimantes", f"Expected 'Imprimantes', got '{printers_label_fr}'"
+
+    # Click the language toggle button
+    page.click("button[title='Toggle language']")
+
+    # Wait for label to update
+    page.wait_for_function(
+        "document.querySelector('nav a[href=\"/printers\"]').textContent.trim() === 'Printers'",
+        timeout=2000,
+    )
+
+    printers_label_en = page.text_content("nav a[href='/printers']").strip()
+    assert printers_label_en == "Printers"
+
+    # Cleanup: reset to fr
+    page.evaluate("localStorage.setItem('imptune_lang', 'fr')")
+
+
+def test_language_persists_across_reload(page, live_server: str) -> None:
+    """After switching to EN, language is preserved on page reload."""
+    page.goto(f"{live_server}/", wait_until="domcontentloaded")
+
+    # Switch to English
+    page.click("button[title='Toggle language']")
+    page.wait_for_function(
+        "document.querySelector('nav a[href=\"/printers\"]').textContent.trim() === 'Printers'",
+        timeout=2000,
+    )
+
+    # Reload
+    page.reload(wait_until="domcontentloaded")
+    page.wait_for_function(
+        "document.querySelector('nav a[href=\"/printers\"]').textContent.trim() !== ''",
+        timeout=3000,
+    )
+
+    label_after_reload = page.text_content("nav a[href='/printers']").strip()
+    assert label_after_reload == "Printers"
+
+    # Cleanup: reset to fr
+    page.evaluate("localStorage.setItem('imptune_lang', 'fr')")
diff --git a/tests/e2e/test_theme_toggle.py b/tests/e2e/test_theme_toggle.py
new file mode 100644
index 0000000..b47f73a
--- /dev/null
+++ b/tests/e2e/test_theme_toggle.py
@@ -0,0 +1,50 @@
+"""UIE-04: E2E tests for theme toggle — data-theme cycling and localStorage persistence."""
+from __future__ import annotations
+import pytest
+
+
+def test_theme_cycles_on_click(page, live_server: str) -> None:
+    """Clicking theme button cycles data-theme attribute: auto -> light -> dark -> auto."""
+    page.goto(f"{live_server}/", wait_until="domcontentloaded")
+
+    # Initial state: auto (default from base.html)
+    initial_theme = page.evaluate("document.documentElement.getAttribute('data-theme')")
+    assert initial_theme == "auto"
+
+    # Click once -> light
+    page.click("button[aria-label='auto']")
+    page.wait_for_function(
+        "document.documentElement.getAttribute('data-theme') === 'light'",
+        timeout=2000,
+    )
+    assert page.evaluate("document.documentElement.getAttribute('data-theme')") == "light"
+
+    # Click again -> dark
+    page.click("button[aria-label='light']")
+    page.wait_for_function(
+        "document.documentElement.getAttribute('data-theme') === 'dark'",
+        timeout=2000,
+    )
+    assert page.evaluate("document.documentElement.getAttribute('data-theme')") == "dark"
+
+
+def test_theme_persists_across_reload(page, live_server: str) -> None:
+    """After clicking theme toggle, the chosen theme is restored on reload."""
+    page.goto(f"{live_server}/", wait_until="domcontentloaded")
+
+    # Switch to light mode
+    page.click("button[aria-label='auto']")
+    page.wait_for_function(
+        "document.documentElement.getAttribute('data-theme') === 'light'",
+        timeout=2000,
+    )
+
+    # Reload the page
+    page.reload(wait_until="domcontentloaded")
+
+    # Theme should still be light (from localStorage)
+    theme_after_reload = page.evaluate("document.documentElement.getAttribute('data-theme')")
+    assert theme_after_reload == "light"
+
+    # Cleanup: reset to auto
+    page.evaluate("localStorage.setItem('imptune_theme', 'auto')")