Add optional language filter on Universe feed

damus/Components/TranslateView.swift

@@ -80,24 +80,7 @@ struct TranslateView: View {
                 currentLanguage = Locale.current.languageCode ?? "en"
             }
 
-            // Rely on Apple's NLLanguageRecognizer to tell us which language it thinks the note is in
-            // and filter on only the text portions of the content as URLs and hashtags confuse the language recognizer.
-            let originalBlocks = event.blocks(damus_state.keypair.privkey)
-            let originalOnlyText = originalBlocks.compactMap { $0.is_text }.joined(separator: " ")
-
-            // Only accept language recognition hypothesis if there's at least a 50% probability that it's accurate.
-            let languageRecognizer = NLLanguageRecognizer()
-            languageRecognizer.processString(originalOnlyText)
-            noteLanguage = languageRecognizer.languageHypotheses(withMaximum: 1).first(where: { $0.value >= 0.5 })?.key.rawValue ?? currentLanguage
-
-            if let lang = noteLanguage, noteLanguage != currentLanguage {
-                // If the detected dominant language is a variant, remove the variant component and just take the language part as translation services typically only supports the variant-less language.
-                if #available(iOS 16, *) {
-                    noteLanguage = Locale.LanguageCode(stringLiteral: lang).identifier(.alpha2)
-                } else {
-                    noteLanguage = NSLocale(localeIdentifier: lang).languageCode
-                }
-            }
+            noteLanguage = event.note_language(damus_state.keypair.privkey) ?? currentLanguage
             
             guard let note_lang = noteLanguage else {
                 noteLanguage = currentLanguage

damus/Models/UserSettingsStore.swift

@@ -128,6 +128,12 @@ class UserSettingsStore: ObservableObject {
         }
     }
 
+    @Published var show_only_preferred_languages: Bool {
+        didSet {
+            UserDefaults.standard.set(show_only_preferred_languages, forKey: "show_only_preferred_languages")
+        }
+    }
+
     @Published var translation_service: TranslationService {
         didSet {
             UserDefaults.standard.set(translation_service.rawValue, forKey: "translation_service")
@@ -210,6 +216,7 @@ class UserSettingsStore: ObservableObject {
         left_handed = UserDefaults.standard.object(forKey: "left_handed") as? Bool ?? false
         zap_vibration = UserDefaults.standard.object(forKey: "zap_vibration") as? Bool ?? false
         disable_animation = should_disable_image_animation()
+        show_only_preferred_languages = UserDefaults.standard.object(forKey: "show_only_preferred_languages") as? Bool ?? false
 
         // Note from @tyiu:
         // Default translation service is disabled by default for now until we gain some confidence that it is working well in production.

damus/Nostr/NostrEvent.swift

@@ -10,6 +10,7 @@ import CommonCrypto
 import secp256k1
 import secp256k1_implementation
 import CryptoKit
+import NaturalLanguage
 
 
 
@@ -259,6 +260,25 @@ class NostrEvent: Codable, Identifiable, CustomStringConvertible, Equatable, Has
         return event_is_reply(self, privkey: privkey)
     }
 
+    func note_language(_ privkey: String?) -> String? {
+        // Rely on Apple's NLLanguageRecognizer to tell us which language it thinks the note is in
+        // and filter on only the text portions of the content as URLs and hashtags confuse the language recognizer.
+        let originalBlocks = blocks(privkey)
+        let originalOnlyText = originalBlocks.compactMap { $0.is_text }.joined(separator: " ")
+
+        // Only accept language recognition hypothesis if there's at least a 50% probability that it's accurate.
+        let languageRecognizer = NLLanguageRecognizer()
+        languageRecognizer.processString(originalOnlyText)
+
+        guard let locale = languageRecognizer.languageHypotheses(withMaximum: 1).first(where: { $0.value >= 0.5 })?.key.rawValue else {
+            return nil
+        }
+
+        // Remove the variant component and just take the language part as translation services typically only supports the variant-less language.
+        // Moreover, speakers of one variant can generally understand other variants.
+        return localeToLanguage(locale)
+    }
+
     public var referenced_ids: [ReferencedId] {
         return get_referenced_ids(key: "e")
     }

damus/Util/LocalizationUtil.swift

@@ -21,3 +21,14 @@ func localizedStringFormat(key: String, locale: Locale?) -> String {
     let fallback = bundleForLocale(locale: Locale(identifier: "en-US")).localizedString(forKey: key, value: nil, table: nil)
     return bundle.localizedString(forKey: key, value: fallback, table: nil)
 }
+
+/**
+ Removes the variant part of a locale code so that it contains only the language code.
+ */
+func localeToLanguage(_ locale: String) -> String? {
+    if #available(iOS 16, *) {
+        return Locale.LanguageCode(stringLiteral: locale).identifier(.alpha2)
+    } else {
+        return NSLocale(localeIdentifier: locale).languageCode
+    }
+}

damus/Views/ConfigView.swift

@@ -153,6 +153,8 @@ struct ConfigView: View {
                 }
 
                 Section(NSLocalizedString("Translations", comment: "Section title for selecting the translation service.")) {
+                    Toggle(NSLocalizedString("Show only preferred languages on Universe feed", comment: "Toggle to show notes that are only in the device's preferred languages on the Universe feed and hide notes that are in other languages."), isOn: $settings.show_only_preferred_languages)
+                        .toggleStyle(.switch)
                     Picker(NSLocalizedString("Service", comment: "Prompt selection of translation service provider."), selection: $settings.translation_service) {
                         ForEach(TranslationService.allCases, id: \.self) { server in
                             Text(server.model.displayName)

damus/Views/SearchHomeView.swift

@@ -7,6 +7,7 @@
 
 import SwiftUI
 import CryptoKit
+import NaturalLanguage
 
 struct SearchHomeView: View {
     let damus_state: DamusState
@@ -14,6 +15,8 @@ struct SearchHomeView: View {
     @State var search: String = ""
     @FocusState private var isFocused: Bool
 
+    let preferredLanguages = Set(Locale.preferredLanguages.map { localeToLanguage($0) })
+    
     var SearchInput: some View {
         HStack {
             HStack{
@@ -41,12 +44,29 @@ struct SearchHomeView: View {
     }
     
     var GlobalContent: some View {
-        return TimelineView(events: model.events, loading: $model.loading, damus: damus_state, show_friend_icon: true, filter: { _ in true })
-            .refreshable {
-                // Fetch new information by unsubscribing and resubscribing to the relay
-                model.unsubscribe()
-                model.subscribe()
+        return TimelineView(
+            events: model.events,
+            loading: $model.loading,
+            damus: damus_state,
+            show_friend_icon: true,
+            filter: {
+                if damus_state.settings.show_only_preferred_languages == false {
+                    return true
+                }
+
+                // If we can't determine the note's language with 50%+ confidence, lean on the side of caution and show it anyway.
+                guard let noteLanguage = $0.note_language(damus_state.keypair.privkey) else {
+                    return true
+                }
+
+                return preferredLanguages.contains(noteLanguage)
             }
+        )
+        .refreshable {
+            // Fetch new information by unsubscribing and resubscribing to the relay
+            model.unsubscribe()
+            model.subscribe()
+        }
     }
     
     var SearchContent: some View {