ICU message formatter used in JS incorrectly handles '{placeholder}' syntax

[rob006]

Current Behavior

Placeholders wrapped between '' should be treated as literal string, so User: '{user}' should be always translated to User: '{user}'. Currently it works correctly if PHP translator is used, but JS translator ignores quoting and replaces placeholders in every case, and produces User: 'rob006'. As a result translators needs to quote differently depending on context - we need User: '{user}' for JS and User: ''{user}'' for PHP. There is no convenient way to know where specific string is used, so this is super inconvenient for languages that use single quote by default. Currently there is ~40 such translations on Weblate: https://weblate.rob006.net/search/flarum/?offset=1&q=target%3Ar%22%27%5C%7B%22&sort_by=context&checksum= and it is hard to say which translations are correct and which should be fixed by replacing ' with ''.

Steps to Reproduce

1. Create User: ''{user}'' translation.

Expected Behavior

Results for $translator->trans('my-key', ['user' => 'rob006']) and app.translator.trans('my-key', { user: 'rob006' }) should be the same: User: 'rob006'.

Screenshots

No response

Environment

• Flarum version: 1.6.2
• PHP version: 7.4.33

Output of php flarum info

No response

Possible Solution

No response

Additional Context

No response