[Translator] Add an option to throw an exception instead of returning the message as is when the translation is not found.

[Crovitche-1623]

For some translations, the id (the key in other words) is the same as the translations (e.g. the Invalid credentials. in the security domain):

export const INVALID_CREDENTIALS = {"id":"Invalid credentials.","translations":{"security":{"fr":"Identifiants invalides.","en":"Invalid credentials.","de":"Fehlerhafte Zugangsdaten.","it":"Credenziali non valide."}}};

Therefore, there is no way in the frontend to distinguish a missing translation from a translation that have the same id (key) same as a translation because the only way I found in the frontend to detect if the translation is missing is checking if the result from the trans method is the same as the id. For example:

const translationConstant = aServiceThat.findConstantById(messageId);

// I'm voluntarily trying in the default domain (`messages`) even though I know the message isn't there.
let translatedMessage = translator.trans(translator[translationConstant]);

if (translatedMessage === translator[translationConstant].id) {
    // Here how I distinguish a missing translation from a translation that have a same value as his id when no exception is thrown. If an exception was thrown, I could try something else (e.g. search in another domain)
}

To solve this problem, I think we could pass an additional to the trans method with a default value (throwWhenNotFound = false) and catch the exception later.

[Kocal]

Hi, thanks for rising this use-case, it actually makes sense and I think I would like to see it in Translator. :)

However, I do not like the fact for trans to accept a new parameter for two reasons:

1. We do not use named parameter, so developers will be forced to pass parameters they probably want to. The translation parameters, the catalogue name, and the locale, in order to pass true to throw if the translation does not exist
2. I don't want trans() from Symfony UX to diverge from the Symfony Translator (PHP), such an option throwWhenNotFound is a no go

A good alternative would be to make this option globally configurable, like _locale with setLocale(), like _localeFallbacks with setLocaleFallbacks().
In the UX Translator Configuration, add a new boolean config like throw_when_not_found (the name can be improved tho), which will be applied to all trans() calls without touching its signature.

WDYT?

[Crovitche-1623]

Yes, that's great. Thanks for the feedback @Kocal. I can try to implement it but it will take some time as I'm not good at JS/TS.

[Kocal]

I can try to implement it but it will take some time as I'm not good at JS/TS.

Don't worry, it should be more simple than what you already did!

However, feel free to ask for help if needed :)