Hi Hydrax,
If your theme doesn’t offer an option to set the font family from the control panel or the Customize panel, then you’ll have to tackle some php code.
The best route would be to create a child theme and add a functions.php file in it. Next, in functions.php, you’ll have to enqueue your own chosen font. If you want to see how this is done in your theme, open functions.php in your parent theme and find the dellow_scripts() function. The very first line inside this function looks like this:
wp_enqueue_style( 'dellow-fonts', '//fonts.googleapis.com/css?family=Lato:400,700,300' );
What you can do in functions.php in your child theme is to create a dellow_child_scripts() function and inside it add your enqueued font replacing Lato with Lato Latin Ext.
I hope this helps ??
– Maria Antonietta.