Change #1192942 had a related patch set uploaded (by Jon Harald Søby; author: Jon Harald Søby):

[mediawiki/core@master] Don't use parsed messages to get numbers in Special:CreateAccount

https://gerrit.wikimedia.org/r/1192942

This was probably caused by e7eecbd9e3f19e7a404abea620f3e0f567b1d697 / T268492.

As a workaround, I think you could just change ->text() to ->plain() here:

					$numberUnescaped = $this->msg( "createacct-benefit-head$benefitIdx" )->text();

This will make it return the wikitext of the messages (e.g. {{NUMBEROFEDITS}}) rather than the number formatted using the wrong language's rules. Later that wikitext will be parsed when it's passed as a parameter to a parsed message, which will use the correct language:

							$this->msg( "createacct-benefit-text$benefitIdx" )->params(
								$numberUnescaped,
								$numberHtml
							)->parse()

This should avoid @Tacsipacsi's concerns about changing the messages, and still fix the issue. For what it's worth, I agree that the messages are used in a weird way in this interface, but we don't have to refactor that to fix this problem.

In T406165#11329286, @matmarex wrote:

This should avoid @Tacsipacsi's concerns about changing the messages, and still fix the issue.

But that wouldn't fix the issue I pointed out in my reply: By changing just the number message on Commons, all other languages than English now say "<number of files> pages".