Converting UTF8 Data to SQL_ASCII
Go to /admin/reports/status and take a look at your unicode library. If you don't have multibyte support, install it: http://php.net/manual/en/mbstring.installation.php

I.e. for ubuntu like systems it's sudo apt-get install php7.0-mbstring for PHP7.

EDIT:

You could try 'auto' instead of 'sql_ascii', and btw., you can skip the count() call and can just write $converted_data[] = drupal_...

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