wiki\extensions\ConfirmAccount\includes\backend\ConfirmAccount.class.php line 114 has

$lang = $user->getOption( 'language' );

however requests submitted on our test wiki in French or German using the portlet in the wiki sidebar created by the LanguageSelector extension sends the email in English the language of the wiki unless I change line 111 to

global $wgContLang, $wgLang;

and line 114 to

$lang = $wgLang->getCode();

while that change does send the email in French, German, or English based on what language was used to request the account, I am not sure that is the correct way to fix the code.

Note that I am not a PHP programmer, but was an IBM Assembler system software developer

Problem was described in the Support Desk as
https://www.mediawiki.org/wiki/Topic:W1yef4cusengmcb2

and is related to T272659: TemporaryPasswordPrimaryAuthenticationProvider does not use the language that the request was created in

trying to change our Request Account to take advantage of the nice capability in the Extension:LanguageSelector that automatically switches the wiki messages to the selected language.

Willing to test the recommended fix.