Dear harris Dimoliatis,
I check your site in Firefox and Chrome, it used font family "Roboto+Condensed&subset=latin,greek-ext,greek"
First, you can add google font in the backend: Roboto+Condensed
Then,you can go to the file: templates\sj_jare25\includes\bottom.php and find:
$doc->addStyleSheet('http://fonts.googleapis.com/css?family='.str_replace(" ","+",$googleWebFont).'');
=> Edit to:
$doc->addStyleSheet('http://fonts.googleapis.com/css?family='.str_replace(" ","+",$googleWebFont). '&subset=latin,greek-ext,greek');
Thanks