Enforce i18n completeness.

locales/ui/en.ftl

@@ -383,3 +383,23 @@ dashboard-and = and
 dashboard-pin = Pin
 common-tabNotImplemented = This area will be implemented in a later milestone.
 editor-noPreviewAvailable = No preview available
+common-operationFailed = { $operation } failed: { $error }
+common-databaseUnavailable = Database unavailable
+common-autoSave = Auto-save
+common-metadataSync = Metadata sync
+common-load = Load
+common-createScript = Create script
+common-createTemplate = Create template
+settings-maxPostsPerPageInvalid = Posts per page must be a valid number
+settings-categoryNameRequired = Category name is required
+settings-categoryAlreadyExists = Category already exists
+siteValidation-summary = { $label }: missing={ $missing }, extra={ $extra }, stale={ $stale }
+engine-readingProjectConfig = Reading project configuration...
+engine-loadingPosts = Loading posts...
+engine-writingCalendar = Writing calendar JSON...
+engine-indexingItem = Indexing: { $current }/{ $total } — { $name }
+engine-checkingItem = Checking: { $current }/{ $total } — { $name }
+engine-renderingPost = Rendering { $post }
+engine-writingGeneratedFiles = Writing generated files
+engine-generationComplete = Site generation complete
+engine-regeneratingItem = Regenerating: { $name }