Attachment with Japanese file name doesn't show

*additional note: Japanese and Chinese characters disappear from the file name sent from Contact Form 7

I’ve got the same problem with Russian Cyrillic filenames.

I found that this plugin make additional filename processing after using wordpress internal function sanitize_file_name().

It cleans all non latin symbols.

So if you don’t want to patch this plugin php-code you should use one more plugin or manually written php-function that can convert you japanese filename into latin symbols or numbers.

Here are some, that I’ve found.
https://www.ads-software.com/plugins/wp-hash-filename/screenshots/
https://www.ads-software.com/plugins/wp-upload-rename/screenshots/

It kills sense of course, but its better anyway then getting empty “.pdf” or “.jpg” filename.

you can also read this topic
https://www.ads-software.com/support/topic/cyrillic-filename-problem?replies=20

As I can see from this code

function wpcf7_canonicalize( $text ) {
	if ( function_exists( 'mb_convert_kana' )
	&& 'UTF-8' == get_option( 'blog_charset' ) ) {
		$text = mb_convert_kana( $text, 'asKV', 'UTF-8' );
	}

	$text = strtolower( $text );
	$text = trim( $text );
	return $text;
}

It seems that this plugin should work with kana right way
So may be you have similar problem with locale on your server as described.