Is it possible that angular serve’s specific translation in development mode?

I followed dev-guide for i18n-merge to apply specific build options for just one locale. But if running ng serve --configuration=en, then the default baseHref is displayed (“http://localhost:4200/de/”) and if I switch to “http://localhost:4200/en/” I got the following messge:

The server is configured with a public base URL of /de – did you mean
to visit /de/en/ instead?

My setup:

$ ng new test --ssr --no-standalone
$ cd test
$ ng add @angular/localize
$ ng add ng-extract-i18n-merge

angular.json:

{
    ...
  "projects": {
    "test": {
      "projectType": "application",
      ...
      "i18n": {
        "sourceLocale": "de",// <---
        "locales": {
          "en": {
            "translation": "src/locale/messages.en.xlf",// <---
                        "baseHref": "/en/"// <---
          }
        }
      },
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:application",
          "options": {
            "localize": true,// <---
            "i18nMissingTranslation": "error",// <---
            "outputPath": "dist/test",
          ...
          },
          "configurations": {
            "production": {
                ...
                        },
            "development": {
              "optimization": false,
              "extractLicenses": false,
              "sourceMap": true,
                            "localize": ["de"],// <---
              "baseHref": "/de/"// <---
                        },
                  "en": {
                    "localize": ["en"] // <---
                  }
          },
          "defaultConfiguration": "production"
        },
        "serve": {
          "builder": "@angular-devkit/build-angular:dev-server",
          "configurations": {
            ...
                        "development": {
              "buildTarget": "test:build:development"
            },
            "en": {
              "buildTarget": "test:build:development,en"// <---
            }
          },
          "defaultConfiguration": "development"
        },
        "extract-i18n": {
          "builder": "ng-extract-i18n-merge:ng-extract-i18n-merge",// "@angular-devkit/build-angular:extract-i18n",
          "options": {
            "buildTarget": "test:build",
                        "format": "xlf2",// <---
                    "outputPath": "src/locale",
                        "targetFiles": ["messages.en.xlf"]// <---
          }
        },
    ...
}