Warning: date() expects parameter 2 to be long, - php

Question

Getting the followoing error:
Warning: date() expects parameter 2 to be long, string given in
/home/users/2/catfood.jp-cybercat/web/academy/wp-includes/functions.php
on line 112
Which points to the line:
$datemonth = $wp_locale->get_month( $datefunc( 'm', $i ) );
What changes are required to the above line to resolve this?
Here is the whole codes
function date_i18n( $dateformatstring, $unixtimestamp = false, $gmt = false ) {
global $wp_locale;
$i = $unixtimestamp;
if ( false === $i ) {
if ( ! $gmt )
$i = current_time( 'timestamp' );
else
$i = time();
// we should not let date() interfere with our
// specially computed timestamp
$gmt = true;
}
/*
* Store original value for language with untypical grammars.
* See https://core.trac.wordpress.org/ticket/9396
*/
$req_format = $dateformatstring;
$datefunc = $gmt? 'gmdate' : 'date';
if ( ( !empty( $wp_locale->month ) ) && ( !empty( $wp_locale->weekday ) ) ) {
$datemonth = $wp_locale->get_month( $datefunc( 'm', $i ) );
$datemonth_abbrev = $wp_locale->get_month_abbrev( $datemonth );
$dateweekday = $wp_locale->get_weekday( $datefunc( 'w', $i ) );
$dateweekday_abbrev = $wp_locale->get_weekday_abbrev( $dateweekday );
$datemeridiem = $wp_locale->get_meridiem( $datefunc( 'a', $i ) );
$datemeridiem_capital = $wp_locale->get_meridiem( $datefunc( 'A', $i ) );
$dateformatstring = ' '.$dateformatstring;
$dateformatstring = preg_replace( "/([^\\\])D/", "\\1" . backslashit( $dateweekday_abbrev ), $dateformatstring );
$dateformatstring = preg_replace( "/([^\\\])F/", "\\1" . backslashit( $datemonth ), $dateformatstring );
$dateformatstring = preg_replace( "/([^\\\])l/", "\\1" . backslashit( $dateweekday ), $dateformatstring );
$dateformatstring = preg_replace( "/([^\\\])M/", "\\1" . backslashit( $datemonth_abbrev ), $dateformatstring );
$dateformatstring = preg_replace( "/([^\\\])a/", "\\1" . backslashit( $datemeridiem ), $dateformatstring );
$dateformatstring = preg_replace( "/([^\\\])A/", "\\1" . backslashit( $datemeridiem_capital ), $dateformatstring );
$dateformatstring = substr( $dateformatstring, 1, strlen( $dateformatstring ) -1 );
}
$timezone_formats = array( 'P', 'I', 'O', 'T', 'Z', 'e' );
$timezone_formats_re = implode( '|', $timezone_formats );
if ( preg_match( "/$timezone_formats_re/", $dateformatstring ) ) {
$timezone_string = get_option( 'timezone_string' );
if ( $timezone_string ) {
$timezone_object = timezone_open( $timezone_string );
$date_object = date_create( null, $timezone_object );
foreach( $timezone_formats as $timezone_format ) {
if ( false !== strpos( $dateformatstring, $timezone_format ) ) {
$formatted = date_format( $date_object, $timezone_format );
$dateformatstring = ' '.$dateformatstring;
$dateformatstring = preg_replace( "/([^\\\])$timezone_format/", "\\1" . backslashit( $formatted ), $dateformatstring );
$dateformatstring = substr( $dateformatstring, 1, strlen( $dateformatstring ) -1 );
}
}
}
}
$j = #$datefunc( $dateformatstring, $i );
/**
* Filter the date formatted based on the locale.
*
* #since 2.8.0
*
* #param string $j Formatted date string.
* #param string $req_format Format to display the date.
* #param int $i Unix timestamp.
* #param bool $gmt Whether to convert to GMT for time. Default false.
*/
$j = apply_filters( 'date_i18n', $j, $req_format, $i, $gmt );
return $j;
}

Answer 1

$datefunc is an alias obviously to php's date method. If that's the case, you are trying to get the month from passing a single integer 1-12. When you can't do that, you need to pass a timestamp to PHP's date method then depending on the attributes you pass as options will return you the following data. Then you are passing it to wordpress locale get_month method that returns the name of the month. You need to refactor your code, so that $i isn't a for loop variable. If you are just trying to get Jan - Dec just do
$i = 1;
$monthArray = [];
do {
// Just push the months to an array and pass it to the view
array_push($monthArray, $wp_locale->get_month($i);
$i++;
} while($i < 13);
Then do what you need to with it. If you are getting a record back from the DB, you need to access the appropriate value in the returned model. Otherwise you're passing an array object. If you are accessing a model you should do)
// Access the property that you intended to retrieve the month on.
$datemonth = $wp_locale->get_month( $datefunc( 'm', $i['published_at'] ) );

Answer 2

I added a plugin called "paid membership pro" and this plugin was written in English and I translated into Japanese. There were lots of codes like this:
<?php printf(__('課金 #%s ( %s )', 'pmpro'), $pmpro_invoice->code, date_i18n(get_option('date_format'), $pmpro_invoice->timestamp));?>
I tried to change these codes as follows:
timestamp), $pmpro_invoice->code );?>
I guess that's why it caused the problem. What do you think?
Now I downloaded the plugin again and there is no problem.
Thank you for helping me.