By default, WordPress sent everything you type when you edit a page to google, “to help you correct your spell”:

In the file wp-includes/js/tinymce/plugins/spellchecker/config.php, you will see the default :

        // General settings
        $config['general.engine'] = 'GoogleSpell';
        //$config['general.engine'] = 'PSpell';
        //$config['general.engine'] = 'PSpellShell';
        //$config['general.remote_rpc_url'] = 'http://some.other.site/some/url/rpc.php';

        // PSpell settings
        $config['PSpell.mode'] = PSPELL_FAST;
        $config['PSpell.spelling'] = "";
        $config['PSpell.jargon'] = "";
        $config['PSpell.encoding'] = "";

        // PSpellShell settings
        $config['PSpellShell.mode'] = PSPELL_FAST;
        $config['PSpellShell.aspell'] = '/usr/bin/aspell';
        $config['PSpellShell.tmp'] = '/tmp';

        // Windows PSpellShell settings
        //$config['PSpellShell.aspell'] = '"c:\Program Files\Aspell\bin\aspell.exe"';
        //$config['PSpellShell.tmp'] = 'c:/temp';

Replace in the first packet of rules Google by pspell (a host working spellchecker) pspell/aspell must be installed on your server,, and the php version you use :

        // General settings
        //$config['general.engine'] = 'GoogleSpell';
        $config['general.engine'] = 'PSpell';
        $config['general.engine'] = 'PSpellShell';
        //$config['general.remote_rpc_url'] = 'http://some.other.site/some/url/rpc.php';