要使用Angular 8和ngx-translate从URL加载翻译JSON文件，你需要遵循以下步骤：

1. 安装ngx-translate：在终端中运行以下命令来安装ngx-translate。

npm install @ngx-translate/core @ngx-translate/http-loader --save

2. 导入ngx-translate模块：在你的Angular模块中导入ngx-translate模块。

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

@NgModule({
  imports: [
    BrowserModule,
    HttpClientModule,
    TranslateModule.forRoot({
      loader: {
        provide: TranslateLoader,
        useFactory: (http: HttpClient) => {
          return new TranslateHttpLoader(http, './assets/i18n/', '.json');
        },
        deps: [HttpClient]
      }
    })
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }

3. 创建一个翻译服务：创建一个名为TranslateService的服务，用于加载和切换语言。

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { TranslateService } from '@ngx-translate/core';

@Injectable({
  providedIn: 'root'
})
export class TranslateLoaderService {
  constructor(private http: HttpClient, private translate: TranslateService) {}

  loadTranslations(lang: string): Promise {
    return new Promise((resolve, reject) => {
      this.http.get(`./assets/i18n/${lang}.json`).subscribe(
        (translations: any) => {
          this.translate.setTranslation(lang, translations);
          this.translate.use(lang);
          resolve();
        },
        (error) => {
          reject(error);
        }
      );
    });
  }
}

4. 加载翻译文件：在应用启动时，使用TranslateLoaderService加载翻译文件。

import { Component } from '@angular/core';
import { TranslateLoaderService } from './translate-loader.service';

@Component({
  selector: 'app-root',
  template: `
    
{{ 'welcome' | translate }}
    English
    French
  `
})
export class AppComponent {
  constructor(private translateLoaderService: TranslateLoaderService) {}

  changeLanguage(lang: string) {
    this.translateLoaderService.loadTranslations(lang);
  }
}

这样，你就可以从URL加载翻译JSON文件并在Angular 8应用程序中使用ngx-translate进行国际化。