Server implementation of the Language Service

server-language.service.ts

import { Inject, Injectable } from '@angular/core';
import { LanguageService, LanguageShortName } from 'somewhere';
import { REQUEST } from '@nguniversal/express-engine/tokens';
import { Request } from 'express';

@Injectable()
export class ServerLanguageService extends LanguageService {
  constructor(@Inject(REQUEST) private request: Request) {
    super();
  }

  getLanguage(defaultLanguage: LanguageShortName): LanguageShortName {
    const preferredLanguage = this.request.headers['accept-language']
      ?.split(',')?.[0]
      ?.substring(0, 2) as LanguageShortName;

    return this.SUPPORTED_LANGUAGES.includes(preferredLanguage)
      ? preferredLanguage
      : defaultLanguage;
  }
}