Angular 9 introduced a global '$localize()' function that needs to be loaded

You need to make sure you have the @angular/localize package first:

npm install @angular/localize --save

Then, import '@angular/localize/init' in your polyfills.ts file just like the error says

The best way if you are using Angular CLI is to run

ng add @angular/localize

It will take care of it automatically

Or else

import '@angular/localize/init'; to your polyfills.ts

Tested with Angular 9

This error started to appear after I upgraded a large Nx/Angular CLI application with multiple sub apps to Angular 10. The solution suggested in the error (Please run ng add @angular/localize from the Angular CLI) does not work if the application contains multiple apps. Each of these auto-generated app had its own polyfill.ts. I manually added the import (import '@angular/localize/init';) in each of the polyfill.ts file. To fix same error while running unit tests, I also had to add the import in test.ts file of libs.

If you have many angular projects in same workspace, running ng add @angular/localize will add import statement import '@angular/localize/init' to polyfills.ts in default Project only,i think this will be fixed in later updates.

so you need to add import '@angular/localize/init' manually to polyfills.ts in other projects.