[i18n]: In case of missing translation generate warning instead of crashing

[mstawick]

I'm submitting a ... (check one with "x")

[X] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior
If translation is missing (ie. I just added new translations but haven't extracted them yet), application will crash with
Translation unavailable for message id="..."

Running in JIT mode.

Expected behavior
Warning is logged in console and message key / predefined missing translation string is rendered.

Reproduction of the problem
Add new i18n key, don't extract messages, start app.

What is the motivation / use case for changing the behavior?
Making development easier / faster. Preventing application from crashing in case of single translation missing.

• Angular version: 2.0.1
• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
  All browsers
• Language: [all | TypeScript X.X | ES6/7 | ES5]
  Typescript
• Node (for AoT issues): node --version =

[vicb]

We could probably add this as an option

I think that this should be default behaviour. Just use the source language if target is empty and issue a warning. Better to read something in a common language (like English, which is not the native language for many people, but anyway understood in most cases), than having an app that crashes.

Another use case would be to omit certain words for translation which are the same for both target and source language (for example localization of an app from en-US to en-GB)

I would restrict the warnings to dev mode though

[cladera]

What's the status of this request?

Angular 2.1.2 still crashes if a message is not present in the translation provider.

Angular 2.2.0 has no reference to i18n in the CHANGELOG.

[feloy]

I also :+1 for a way to soft-handle these missing translated message.

Having an error is blocking continuous integration as translations cannot be raisonably committed at the same time as the add of i18n "directive".

[marclaval]

Fixed by #14113

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