XML Files Can Have Any Character Encoding

XML files can be saved with any character encoding. That character encoding should be defined at the top of the XML file, per XML standards on specifying the character encoding of an XML document.

If special characters in your XML file aren’t appearing correctly in the posts created by WP All Import, it means that the encoding specified in your XML file is probably incorrect – maybe your XML file is claiming to be a UTF-8 when it really is a Windows-1252, or similar.

If you're sure that your XML file is valid, it's not using UTF-8 encoding, and WP All Import is still rejecting it, try adding this code snippet inside your child theme's functions.php file (or in a plugin like Code Snippets):

 add_filter( 'is_xml_preprocess_enabled', 'wpai_is_xml_preprocess_enabled', 10, 1 );
function wpai_is_xml_preprocess_enabled( $is_enabled ) {
    return false;
}

CSV Files Must Be UTF-8 Or UTF-8 Compatible

Since there is no way to specify the character encoding for a CSV file, WP All Import just assumes all uploaded CSV files are UTF-8, which is the standard character encoding for the web.

This works the vast majority of the time, but if you are importing a CSV file with special characters (things like umlauts, non-Latin characters, etc.) and those special characters aren’t appearing correctly in the posts created by WP All Import, try opening your CSV file in a text editor using the correct encoding, and then re-save it using UTF-8.

On a Mac, our favorite way to do this is using Sublime Text 2.