Ability of variable in localized string

### Which @angular/* package(s) are relevant/related to the feature request?

@angular/angular, as in latest version

### Description

Since the localize feature is present in Angular, we are allow to use variable in localize string, and it works well from the time I start to play with Angular.

But now I have a special situation: I have a string that does not need variable in the base language, as known as source in the .xlf file, but the string need to use a variable when translate to english to make the UX better, seems like it cannot be done because I cannot access component itself without having any varable in source string

### Proposed solution

I don't really have a proper solution at this point, I'm totally ok with any solution that can perfectly solve this problem

### Alternatives considered

Seems like there are no other way to solve this problem

Start by reviewing Angular's localize feature and how variables are represented in source and translated .xlf strings. Clarify how a translation can introduce a variable absent from the base-language string, then define acceptance cases for the English translation and other languages before proposing a solution.

Written by the indexing model from the issue text.