如何在PHP中显示自定义错误消息？

I am trying to limit file upload size on my site and using the following code (which works fine):

function limit_upload_size( $file ) {

// Set the desired file size limit
$file_size_limit = 1024; // 1MB in KB

// exclude admins
if ( ! current_user_can( 'manage_options' ) ) {

    $current_size = $file['size'];
    $current_size = $current_size / 1024; //get size in KB

    if ( $current_size > $file_size_limit ) {
        $file['error'] = sprintf( __( 'ERROR: File size limit is %d KB.' ), $file_size_limit );
    }

}

return $file;

}
add_filter ( 'wp_handle_upload_prefilter', 'limit_upload_size', 10, 1 );

The only problem I've encountered is that the error message doesn't display. When I change

$file['error'] = sprintf( __( 'ERROR: File size limit is %d KB.' ), $file_size_limit );

to

 $file['error'] = sprintf( __e( 'ERROR: File size limit is %d KB.' ), $file_size_limit );

I see the following error message instead: Error #-200: HTTP Error instead of the custom error message.

What is wrong with this code?

Thanks in advance!

That's because __() returns the translated text, while _e() displays/echos it. And as you are inside sprintf() function, you need the returned translated text, not display it to the screen.

_e() codex reference, __() codex reference

Thanks.