diff --git a/src/gui/app.py b/src/gui/app.py
index bc6b00d..50028bb 100644
--- a/src/gui/app.py
+++ b/src/gui/app.py
@@ -148,7 +148,7 @@ def _home_page() -> None:
 # the entries; an empty-string key suppresses the header so the Home
 # entry sits at the top without a label above it.
 
-from src.gui.tools_registry import TOOLS, section_label  # noqa: E402
+from src.gui.tools_registry import TOOLS, section_label, tool_name  # noqa: E402
 from src.i18n import t as _t  # noqa: E402
 
 
@@ -167,13 +167,16 @@ def _build_navigation() -> dict[str, list]:
         "transformations": [],
         "automations": [],
     }
+    # Resolve the tool name through ``tool_name`` (i18n lookup) instead
+    # of using the registry's English ``tool.name`` field, otherwise the
+    # sidebar stays in English when the user switches to Spanish.
     for tool in TOOLS:
         by_section[tool.section].append(
             _page_for(
                 tool.tool_id,
                 page_slug=tool.page_slug,
                 icon=tool.icon,
-                title=tool.name,
+                title=tool_name(tool.tool_id),
             )
         )