I can confirm what @JB Nizet is referring to in his answer is now working in Angular 9, so this works:
foo() {
const appTitle = $localize`:@@siteTitle:Example Title`;
// appTitle is now translated based on locale
titleService.setTitle(appTitle);
}
You can read more about it here https://github.com/angular/angular/blob/master/packages/localize/init/index.ts