vue-cli/packages/@vue/cli/lib/generators/babel/index.js

module.exports = api => {
  api.onPromptComplete(options => {
    if (!options.features.includes('ts')) {
      api.extendPackage({
        devDependencies: {
          '@vue/cli-plugin-babel': '^1.0.0',
          'babel-preset-vue-app': '^2.0.0'
        }
      })
      api.renderFiles('./files')
    }
  })
}