Bundle does not work properly with new Intl ICU translations

[bocharsky-bw]

1. When I extract translations with $ bin/console translation:extract - the command put Intl ICU translations to the standard messages.en.xlf files instead of messages+intl-icu.en.xlf.
2. Even when I have "Intl ICU" translations in messages+intl-icu.en.xlf - the $ bin/console translation:extract command put those translations into messages.en.xlf anyway, i.e. so I have duplications in both files.
3. Xliff format does not support + sign in file ID, i.e: <file id="messages+intl-icu.en"> is invalid ID, at least PhpStorm says so:

4. The Web UI, i.e. `/admin/_trans/app` page does not display translations of `messages+intl-icu.en.xlf` as a separate domain, it displays them in `messages` domain. But if you edit those messages, they popup in messages.en.xlf 5. Probably something else...

[Guite]

Point 2 is solved by php-translation/symfony-storage#49 and symfony/symfony#35430

Point 1 is still a huge problem though. It would be great if the extractor could be enforced to append the +intl-icu suffix to all domains.

[tristanbes]

Hey @Guite ; Just came accross the issue after discovering that translating a plural string has changed starting from Symfony 4.2

The problem is that it will render the string "as is" without the plural form
Outputs:

{COUNT, PLURAL, =0 {THERE ARE NO APPLES} ONE {THERE IS ONE APPLE...} OTHER {THERE ARE # APPLES!}}

and I didn't find in the documentation if there is any specific steps that I need to do to achieve what is done in the Symfony documentation (https://symfony.com/doc/4.4/translation/message_format.html#pluralization)

Steps to reproduce

// messages.en.xlf updated from the web-ui
<?xml version="1.0" encoding="utf-8"?>
<xliff xmlns="urn:oasis:names:tc:xliff:document:2.0" version="2.0" srcLang="fr" trgLang="en">
  <file id="messages.en">
    <unit id="bu5PltH" name="example">
      <notes>
        <note category="file-source" priority="1">app/templates/ex/show.html.twig:219</note>
        <note category="state" priority="1">new</note>
      </notes>
      <segment>
        <source>example</source>
        <target>{count, plural, =0 {There are no apples} one {There is one apple...} other {There are # apples!}}</target>
      </segment>
    </unit>

{{ "example"|trans({'%count%': 3}) }}