[i18n] ability to dynamically load translations for the app

Start with @angular/localize and the linked v8 JIT i18n documentation; compare the v9 loadTranslations API with the requested XLIFF and runtime-locale workflow. Done means there is a supported approach for switching locales during development, including how XLIFF data is handled.

🐞 bug report

Affected Package

@angular/localize

Is this a regression?

Yes, it's a regression from v8

Description

In v8 was a very handy solution to load your translation data for development.
It's described on this documentation page https://v8.angular.io/guide/i18n#merge-with-the-jit-compiler

With the migration to v9 there's no corresponding solution that will allow to quickly switch locales during runtime for development. As far as I understand, the suggested replacement is to run ng serve with the desired locale every time.

A little bit background here. We have 2 applications, every with 4 languages. For production, we build it with AOT as suggested. For development we use JIT and load corresponding translation depending on the browser URL (German for /de/ for example), this mimics prod behavior. So, to switch translation and check how the interface looks in a different language, you just need to pick up another item in the language menu. The page reloads at the same URL but with a different language. Starting from v9 it's not supported, so we would have to run ng serve every time for a new language and start from the home page for every language again.

What would be a suggested way repeat v8 behavior? I checked loadTranslatios but it accepts a key-value object, not a XLIFF data. Is any function that can transform from XLIFF to a format understandable for loadTranslations

🌍 Your Environment

Angular Version:

Angular CLI: 9.1.9
Node: 12.4.0
OS: darwin x64

Angular: 9.1.11
... animations, common, compiler, compiler-cli, core, forms
... language-service, localize, platform-browser
... platform-browser-dynamic, router
Ivy Workspace: Yes

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.901.9
@angular-devkit/build-angular      0.901.9
@angular-devkit/build-ng-packagr   0.901.9
@angular-devkit/build-optimizer    0.901.9
@angular-devkit/build-webpack      0.901.9
@angular-devkit/core               9.1.9
@angular-devkit/schematics         9.1.9
@angular/cdk                       9.2.4
@angular/cli                       9.1.9
@angular/material                  9.2.4
@angular/material-moment-adapter   9.2.4
@ngtools/webpack                   9.1.9
@schematics/angular                9.1.9
@schematics/update                 0.901.9
ng-packagr                         9.1.5
rxjs                               6.5.5
typescript                         3.8.3
webpack                            4.42.0