functions.php

function google_fonts() {
	$query_args = array(
		'family' => 'Open+Sans:400,700|Oswald:700'
		'subset' => 'latin,latin-ext',
	);
	wp_register_style( 'google_fonts', add_query_arg( $query_args, "//fonts.googleapis.com/css" ), array(), null );
            }
            
add_action('wp_enqueue_scripts', 'google_fonts');

There should be a comma "," between items in $query_args array, not at the end:

'family' => 'Open+Sans:400,700|Oswald:700',
        'subset' => 'latin,latin-ext'

@hocu Yup, I can confirm that. The above example will throw an error, your´s won´t. Thx.