SwiftUI设置UserDefaults切换语言后，本地化字符串如何生效？

一、无需重启：实现即时语言切换 #

直接修改AppleLanguages后，SwiftUI的LocalizedStringKey不会自动刷新——因为它是在视图初始化时读取语言配置的。要实现即时生效，需要自定义本地化管理工具：

1. 自定义本地化管理器 #

创建可观察的管理器类，负责读取当前语言并提供本地化字符串：

import SwiftUI

class LocalizationManager: ObservableObject {
    static let shared = LocalizationManager()
    
    @Published var currentLanguage: Language {
        didSet {
            UserDefaults.standard.set([currentLanguage.rawValue], forKey: "AppleLanguages")
            objectWillChange.send()
        }
    }
    
    private init() {
        let savedLang = UserDefaults.standard.string(forKey: "AppleLanguages")?.first ?? "en"
        currentLanguage = Language(rawValue: savedLang) ?? .en
    }
    
    func localize(_ key: String) -> String {
        let path = Bundle.main.path(forResource: currentLanguage.rawValue, ofType: "lproj")!
        let bundle = Bundle(path: path)!
        return NSLocalizedString(key, bundle: bundle, comment: "")
    }
}

extension Language {
    var displayName: String {
        LocalizationManager.shared.localize(
            self.rawValue == "en" ? "english" : self.rawValue == "uk" ? "ukraine" : "russian"
        )
    }
}

2. 修改语言切换逻辑 #

替换原switchLanguage方法，改为更新管理器的当前语言：

func switchLanguage(to language: Language) {
    LocalizationManager.shared.currentLanguage = language
}

3. 更新LanguageView视图 #

将所有LocalizedStringKey替换为自定义本地化方法，让视图监听语言变化：

struct LanguageView: View {
    @ObservedObject private var localizationManager = LocalizationManager.shared
    @Injected private var userDefaultsManager: UserDefaultsManaging
    @State private var showingAlert = false
    @State var selected: Language?
    @State var original: Language?
    
    var body: some View {
        ZStack {
            AppBackground()
            List {
                Section(localizationManager.localize("language")) {
                    languageButton(to: .en)
                    languageButton(to: .ru)
                    languageButton(to: .uk)
                }
            }
            .scrollContentBackground(.hidden)
        }
        .alert(localizationManager.localize("change_language_message"), isPresented: $showingAlert) {
            Button(localizationManager.localize("choose")) {
                userDefaultsManager.switchLanguage(to: selected ?? .en)
            }
            Button(localizationManager.localize("cancel"), role: .cancel) {
                withAnimation(.easeIn) {
                    selected = original ?? .en
                }
            }
        }
        .navigationTitle(localizationManager.localize("change_language"))
        .onAppear {
            self.original = userDefaultsManager.getLanguage()
            self.selected = userDefaultsManager.getLanguage()
        }
    }
    
    @ViewBuilder func languageButton(to language: Language) -> some View {
        Button {
            withAnimation(.easeIn) {
                if selected != language {
                    selected = language
                    showingAlert = true
                }
            }
        } label: {
            HStack {
                Text(language.displayName)
                if selected == language {
                    Spacer()
                    Image(systemName: "checkmark")
                }
            }
            .foregroundColor(.jmkBlue)
            .fontWeight(selected == language ? .semibold : .regular)
        }
    }
}

修改后，切换语言时所有使用localize()方法的文本会自动刷新，无需重启。

二、如果必须重启应用的实现方式 #

iOS没有官方重启API，可通过以下两种方式实现：

1. 模拟重启（推荐） #

重新设置App的根视图，模拟重启效果：

func restartApp() {
    guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
          let window = windowScene.windows.first else { return }
    
    let rootView = ContentView() // 替换为你的初始根视图
    window.rootViewController = UIHostingController(rootView: rootView)
    window.makeKeyAndVisible()
    
    UIView.transition(with: window, duration: 0.5, options: .transitionCrossDissolve, animations: nil)
}

在Alert确认按钮中调用：

Button(localizationManager.localize("choose")) {
    userDefaultsManager.switchLanguage(to: selected ?? .en)
    restartApp()
}

2. 强制退出（不推荐） #

使用exit(0)强制退出应用，用户需手动重新打开，体验较差，且可能引发审核关注：

func forceRestart() {
    exit(0)
}

内容的提问来源于stack exchange，提问作者Jan Janovec