Your integration URL needs {{}} for the parameters subject to url interpolation.
That would be: http://localhost:3000?language={{pcLangTag}}&environment={{pcEnvironment}}
See here for URL interpolation
Your call to ClientApp constructor seems also incorrect.
let thisApp = new ClientApp({
pcEnvironmentQueryParam: 'environment'
});
Not stupid.
There are places where the double {{xxxx}} is missing - only one set of {} appears. This is/was due to automatic formatting on the doc site. The link I provided below is one of the pages which gives and displays the proper format.