diff --git a/oAI/ViewModels/ChatViewModel.swift b/oAI/ViewModels/ChatViewModel.swift
index ecc2dc8..7b3f88e 100644
--- a/oAI/ViewModels/ChatViewModel.swift
+++ b/oAI/ViewModels/ChatViewModel.swift
@@ -90,6 +90,7 @@ You are a helpful AI assistant. Follow these core principles:
 - **Be Direct**: Provide concise, relevant answers. No unnecessary preambles.
 - **Show Your Work**: If you use capabilities (tools, web search, etc.), demonstrate what you did.
 - **Complete Tasks Properly**: If you start something, finish it correctly.
+- **Match the User's Language**: Always reply in the same language the user is writing in, even when the request itself involves another language (e.g. a translation or spelling request) — the target language applies to the content you produce, not to your own reply.
 
 ## FORMATTING
 
diff --git a/oAI/Views/Main/ContentView.swift b/oAI/Views/Main/ContentView.swift
index a823094..f2d740b 100644
--- a/oAI/Views/Main/ContentView.swift
+++ b/oAI/Views/Main/ContentView.swift
@@ -29,7 +29,8 @@ import Darwin   // uname, sysctlbyname
 struct ContentView: View {
     @Environment(ChatViewModel.self) var chatViewModel
     private var updateService = UpdateCheckService.shared
-    @State private var columnVisibility: NavigationSplitViewVisibility = .all
+    @State private var columnVisibility: NavigationSplitViewVisibility =
+        SettingsService.shared.sidebarVisible ? .all : .detailOnly
     @State private var showIntelWarning = false
 
     var body: some View {
@@ -46,6 +47,9 @@ struct ContentView: View {
             )
         }
         .frame(minWidth: 860, minHeight: 560)
+        .onChange(of: columnVisibility) { _, newValue in
+            SettingsService.shared.sidebarVisible = newValue != .detailOnly
+        }
         #if os(macOS)
         .onAppear {
             NSApplication.shared.windows.forEach { $0.tabbingMode = .disallowed }
diff --git a/oAI/Views/Screens/SettingsView.swift b/oAI/Views/Screens/SettingsView.swift
index 809667b..5911fee 100644
--- a/oAI/Views/Screens/SettingsView.swift
+++ b/oAI/Views/Screens/SettingsView.swift
@@ -125,6 +125,7 @@ You are a helpful AI assistant. Follow these core principles:
 - **Be Direct**: Provide concise, relevant answers. No unnecessary preambles.
 - **Show Your Work**: If you use capabilities (tools, web search, etc.), demonstrate what you did.
 - **Complete Tasks Properly**: If you start something, finish it correctly.
+- **Match the User's Language**: Always reply in the same language the user is writing in, even when the request itself involves another language (e.g. a translation or spelling request) — the target language applies to the content you produce, not to your own reply.
 
 ## FORMATTING