要在Angular 7中实现语言切换功能，可以使用@ngx-translate/core库与localize-router库的结合。以下是一个示例解决方案：

1. 首先，安装所需的库：

npm install @ngx-translate/core @ngx-translate/http-loader localize-router

2. 在app.module.ts文件中，导入所需的模块和服务：

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpClient, HttpClientModule } from '@angular/common/http';
import { TranslateModule, TranslateLoader } from '@ngx-translate/core';
import { TranslateHttpLoader } from '@ngx-translate/http-loader';
import { LocalizeRouterModule } from 'localize-router';
import { LocalizeRouterHttpLoader } from 'localize-router-http-loader';

import { AppComponent } from './app.component';

// AoT requires an exported function for factories
export function HttpLoaderFactory(http: HttpClient) {
  return new TranslateHttpLoader(http);
}

export function localizeLoaderFactory(http: HttpClient) {
  return new LocalizeRouterHttpLoader(http, './assets/i18n/');
}

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    HttpClientModule,
    TranslateModule.forRoot({
      loader: {
        provide: TranslateLoader,
        useFactory: HttpLoaderFactory,
        deps: [HttpClient]
      }
    }),
    LocalizeRouterModule.forRoot([
      {
        path: '',
        redirectTo: '/home',
        pathMatch: 'full'
      },
      {
        path: 'home',
        loadChildren: './home/home.module#HomeModule'
      }
    ], {
      parser: {
        provide: LocalizeParser,
        useFactory: localizeLoaderFactory,
        deps: [HttpClient]
      }
    })
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

3. 在app.component.ts文件中，导入所需的模块和服务，并在构造函数中加载语言文件：

import { Component } from '@angular/core';
import { TranslateService } from '@ngx-translate/core';
import { Location } from '@angular/common';
import { LocalizeRouterService } from 'localize-router';

@Component({
  selector: 'app-root',
  template: `
    
{{ 'HOME.TITLE' | translate }}
    English
    French
    German
    

    
  `,
  styles: []
})
export class AppComponent {
  constructor(
    private translate: TranslateService,
    private location: Location,
    private localize: LocalizeRouterService
  ) {
    translate.setDefaultLang('en');
    translate.use('en');
  }

  switchLanguage(language: string) {
    this.translate.use(language);
    this.localize.changeLanguage(language);
    this.location.replaceState(this.localize.translateRoute(this.location.path()));
  }
}

4. 在home.component.ts文件中，使用translate管道来翻译文本：

import { Component } from '@angular/core';
import { TranslateService } from '@ngx-translate/core';

@Component({
  selector: 'app-home',
  template: `
    
{{ 'HOME.WELCOME' | translate }}
    
{{ 'HOME.DESCRIPTION' | translate }}
  `,
  styles: []
})
export class HomeComponent {
  constructor(private translate: TranslateService) { }
}

5. 在assets/i18n文件夹下，创建语言文件（例如en.json、fr.json、de.json）：

en.json:

{
  "HOME": {
    "TITLE": "Home",
    "WELCOME": "Welcome to my website!",
    "DESCRIPTION": "This is a sample application for language switching."
  }
}

fr.json:

{
  "HOME": {
    "TITLE": "Accueil",
    "WELCOME": "Bienvenue sur mon site Web!",
    "DESCRIPTION": "Ceci est une application de démonstration pour le changement de langue."
  }
}

de.json:

{
  "HOME": {
    "TITLE": "Startseite",
    "WELCOME": "Willkommen auf meiner Webseite!",
    "DESCRIPTION": "Dies ist eine Beispielanwendung zum Sprachwechsel."
  }
}

这样，你就可以在Angular 7中实现语言切换功能了。通过点击按钮切换语言，应用程序