MainWindow.xaml is one large window with all pages. Its code is split into partial classes under Xenvious/MainWindow/, one file per page or concern:

MainWindow.Dashboard.cs / DashboardPage.cs   dashboard, status strip, launch creator
MainWindow.Props.cs / DynamicProps.cs         prop lists
MainWindow.Race*.cs                           race settings, checkpoints, vehicles
MainWindow.Mission.*.cs                       mission (LTS/Capture) rules, teams, actors, zones, ...
MainWindow.Misc.*.cs                          copy jobs, map mover, menu switcher, script patches
MainWindow.Settings.cs                        settings and language
MainWindow.Navigation.cs                      page switching
MainWindow.Dialog.cs / ScreenMessage.cs       in-app dialog and toasts

When you add a page, add a new partial file named after it (MainWindow.<Page>.cs) with a first-line comment saying what it covers, like the existing files. Keep game logic out of it; put that in Creator Classes/.

Reusable controls and styles are in Controls/ (ComboBox.xaml, Checkbox.xaml, Slider.xaml, CustomTB, WeaponInventoryControl, ...). Use them instead of plain WPF controls so the look stays consistent.

WPF styling pitfalls seen here: an explicit Style replaces the implicit one, so derive with BasedOn and define it after its base; a custom control template needs its ContentPresenter; and do not steal focus from the game, show an in-app dialog (MainWindow.Dialog.cs) instead.

All UI text goes through Translation/Translation.cs. It holds one dictionary per language:

MainWindow.Translation is the active dictionary (_Language.FromCode(...), set in MainWindow.Settings.cs). A missing key shows "missing translation".

In XAML:

<TextBlock Text="{Binding Translation[jobimg], FallbackValue=Job Image}" />

In code: Translation["key"]. View models get a translate function (_t("key", "fallback")).

Rule: a new key goes into all six dictionaries in the same commit. If you cannot translate, use the English text in the other languages and say so in the PR, so a native speaker can fix it.

Short, plain words that say what a control does. Status and error lines describe what happened and what to do next, not internal names.