I need change fonts in theme with correct Slovak diacritics

The theme uses Google Web-Fonts, you should select font style #3 (Roboto + Arial, I think both support those characters) in Customizer.

The current font you are using is Montserrat + Source Sans Pro.

dear acosmin thank you for quick reply …

I was try all combinations, but there is some trouble with some characters, especially ???ň…

When I need completely change font type for other Google font set, how must I continue ?

It’s a bit complicated, which fonts do you want?

I don′t know exactly because this will decide my customer, but for example this is possible?

https://www.google.com/fonts/specimen/Lobster

or some other which is no standard arial or times new romans .. this site is planned for children with creative interests that fonts may be some “creative” but with correct diacritics

You should be able to include fonts from functions.php, lines:

/*  Font Families
/* ------------------------------------ */
if ( ! function_exists( 'ac_font_url' ) ) {

	function ac_font_url( $font_type = 'style1' ) {

		// You have 4 optios
		// Please select a option from the WP Theme Customise, Content tab.
		$font_url = '';
		$google_fonts_url = "//fonts.googleapis.com/css";

		if( $font_type == 'style1' ) {
			$font_url = add_query_arg( 'family', urlencode( 'Montserrat:400,700|Questrial|Arimo:400,700|Source Sans Pro:400,700,400italic,700italic' ), $google_fonts_url );
		} elseif( $font_type == 'style2' ) {
			$font_url = add_query_arg( 'family', urlencode( 'PT Serif:400,700,400italic,700italic|Montserrat:400,700|Questrial' ), $google_fonts_url );
		} elseif( $font_type == 'style3' ) {
			$font_url = add_query_arg( 'family', urlencode( 'Roboto:400,700italic,700,400italic|Montserrat:400,700|Questrial' ), $google_fonts_url );
		} elseif( $font_type == 'style4' ) {
			$font_url = add_query_arg( 'family', urlencode( 'PT Sans:400,700,400italic,700italic' ), $google_fonts_url );
		}

		return $font_url;

	}

}

You need to add fonts only to style #1 and then change the necessary lines in style.css, more exactly:

body, .post-template-1 .details .detail em, .single-template-1 .details detail em, textarea, input, select, .about-share, .logo .description, .content-wrap .review-wrap-up, .content-wrap #review-statistics .review-wu-bars h3, .content-wrap .review-wu-bars span, .content-wrap #review-statistics .review-wrap-up .review-wu-right ul li, .comments-area #cwp-slider-comment .comment-form-meta-option label {
	/* Same Font - Source Sans Pro */
	font-family: 'Source Sans Pro', sans-serif;
}
.menu-main,  .browse-more, .sidebar-heading, .tabs-widget-navigation, .post-template-1 .title, .single-template-1 .title, .sidebar .social-btn, .ac-popular-posts .position, .ac-popular-posts .title, .ac-featured-posts .thumbnail .details .title, .ac-ad-title-300px, .posts-pagination .paging-wrap, .page-links-wrap .page-links, .comments-pagination .paging-wrap, .footer-credits .copyright, .browse-by-title, #wp-calendar tbody td, #wp-calendar thead th, #wp-calendar #prev, #wp-calendar #next, .single-content h1, .single-content h2, .single-content h3, .single-content h4, .single-content h5, .single-content h6, .comment-text h1, .comment-text h2, .comment-text h3, .comment-text h4, .comment-text h5, .comment-text h6, .ac-recent-posts .title, .sidebar #recentcomments li a, .slider .title, .about-share .title, .comments-title, .comment-main .vcard .fn, .comment-reply-title, .form-submit input[type=submit], .page-404 h1, .main-page-title, .menu-wrap .search-field, .menu-wrap .search-submit, .banner-small-title, .post-thumbnail .sticky-badge, .no-comments, .content-wrap #review-statistics .review-wrap-up .review-wu-right h2, .content-wrap #review-statistics h1, .content-wrap #review-statistics h2, .content-wrap #review-statistics h3, .content-wrap #review-statistics h4, .content-wrap #review-statistics h5, .content-wrap #review-statistics h6, .content-wrap  #review-statistics .cwp-review-percentage span, .content-wrap .cwp-item-price, .content-wrap .affiliate-button a span
{
	/* Same Font - Montserrat */
	font-family: 'Montserrat', sans-serif;
}
.logo, .footer-credits .blog-title {
	/* Same Font - Questrial */
	font-family: 'Questrial', sans-serif;
}
.ac-featured-posts .category, .ac-recent-posts .category, .slider .details .info, .comments-number, .post-template-1 .details .detail, .single-template-1 .details, .detail, .ac-popular-posts .category, .ac-twitter-tweet-time, .post-template-1 .details .p-share .contents em, .sidebar #recentcomments a.url, .sidebar #recentcomments, .comments-title .comments-number, .comment-main .vcard .comm-edit, .comment-main .comment-reply-link, label {
	/* Same Font - Arimo */
	font-family: 'Arimo', sans-serif;
}