Is there any reason to do this besides "it will look like it is PHP"?

That and to make the correct behavior be the simple(st) way of writing code.

The coding style that's emerged for this is mw.language.convertNumber.

// plain parameters
mw.msg( key, thing );
//> "Hello $1" => "Hello Thing"

// number parameter
mw.msg( key, mw.language.convertNumber( edits ) );
//> "$1 edits" => "1,024 edits"

This separates the concerns of message formatting and value formatting, avoids extra dependencies, and I think is much easier to understand by not having to know the special method for a certain thing in addition to learning the "normal" way to do it for other scenarios.

If there was a common problem to avoid or some deeper integration that plain calls can't provide, I would agree there is added value, but in its current form, I think this is all we need?

If one first uses mw.language.convertNumber before passing to mw.msg like here, https://github.com/wikimedia/mediawiki-extensions-ContentTranslation/blob/a861b0256ae4999b6f5998fd3e40c44ee5deaf94/modules/tools/mw.cx.tools.IssueTrackingTool.js#L287-L292 will a plural message like {{PLURAL:$1|$1 warning|$1 warnings}} parse and analysis native digits like ۱ ۲ ۳ just like 1 2 3? The JS counterpart should've followed the same pattern as PHP one

In T57775#9979277, @Ebrahim wrote:

If one first uses mw.language.convertNumber before passing to mw.msg like here, https://github.com/wikimedia/mediawiki-extensions-ContentTranslation/blob/a861b0256ae4999b6f5998fd3e40c44ee5deaf94/modules/tools/mw.cx.tools.IssueTrackingTool.js#L287-L292 will a plural message like {{PLURAL:$1|$1 warning|$1 warnings}} parse and analysis native digits like ۱ ۲ ۳ just like 1 2 3? The JS counterpart should've followed the same pattern as PHP one

Yes, that works correctly, as the parameter to {{PLURAL:}} in JavaScript is converted back to a plain number first, using mw.language.convertNumber( ..., true ): https://gerrit.wikimedia.org/g/mediawiki/core/+/5b6a8374360032a41832c2e9cb2cba6590a20fa7/resources/src/mediawiki.jqueryMsg/mediawiki.jqueryMsg.js#1232 (it's a bit inelegant that this is how it works, but… it works)

@matmarex I didn't know, it was surprising, thanks, uploaded a patch to use that then https://gerrit.wikimedia.org/r/c/mediawiki/extensions/ContentTranslation/+/1054064 😊