add(ui/ux): german and english ui with a toggle in the navbar

tests/test_ui_dialogs.py

@@ -57,12 +57,14 @@ def server(tmp_path_factory):
 
 @pytest.fixture
 def page(server):
+    """A German browser, so the UI language is the same everywhere."""
     with sync_api.sync_playwright() as pw:
         try:
             browser = pw.chromium.launch()
         except Exception as exc:  # browsers not downloaded
             pytest.skip(f"no chromium: {exc}")
-        page = browser.new_page(viewport={"width": 1200, "height": 900})
+        page = browser.new_page(viewport={"width": 1200, "height": 900},
+                                locale="de-DE")
         errors = []
         page.on("pageerror", lambda e: errors.append(str(e)))
         page.goto(server, wait_until="networkidle")
@@ -124,3 +126,30 @@ def test_format_tags_and_the_format_filter(page):
     rows = page.locator("#import-table tbody tr")
     assert rows.count() == 1
     assert "epub" in rows.first.locator(".tag.fmt").text_content()
+
+
+def test_the_browser_language_decides_and_the_toggle_switches(page, server):
+    assert page.locator("nav button[data-view=search]").text_content() == "Suche"
+    assert page.locator("#lang-toggle").text_content() == "EN"
+
+    page.click("#lang-toggle")
+    assert page.locator("nav button[data-view=search]").text_content() == "Search"
+    assert page.locator("#lang-toggle").text_content() == "DE"
+    assert page.get_attribute("html", "lang") == "en"
+    assert page.get_attribute("#search-q", "placeholder") == "Title, author or ISBN…"
+
+    page.reload(wait_until="networkidle")  # the choice outlives the reload
+    assert page.locator("nav button[data-view=search]").text_content() == "Search"
+
+
+def test_english_reaches_the_rendered_rows(page):
+    page.click("#lang-toggle")
+    page.click("nav button[data-view=import]")
+    page.click("#scan-btn")
+    page.wait_for_selector("[data-quick]")
+    assert "— skip —" in page.locator("#import-table tbody select").first.text_content()
+    assert "2.0 KB" in " ".join(page.locator("#import-table .tag.fmt").all_text_contents())
+    # switching back re-renders the table that is already on screen
+    page.click("#lang-toggle")
+    assert "— überspringen —" in page.locator("#import-table tbody select").first.text_content()
+    assert "2,0 KB" in " ".join(page.locator("#import-table .tag.fmt").all_text_contents())