Add active class to WordPress nav - php

Question

I have pretty long nav here, which I have to import to WordPress.
<header class="small">
<div class="yellow-stripe"></div>
<div class="container">
<nav role="navigation">
<ul class="navigation">
<li>
About us
<ul class="sub-navigation">
<li>We are</li>
<li>Our story</li>
<li>Why Ledil</li>
<li>Where</li>
<li>Management</li>
<li>Investors</li>
</ul>
</li>
<li>News</li>
<li>Events</li>
<li>FAQ</li>
</ul>
</nav>
<ul class="lang">
<li class="active">EN</li>
<li>ES</li>
<li>RUS</li>
</ul>
</div>
<div class="nav-button">
<div class="line"></div>
<div class="line"></div>
<div class="line"></div>
</header>
It's made in HTML and now I have to import it to WordPress. I got WordPress to include the header, and to load the whole thing just fine, and it looks great on page, but I would need to add class="active" for bootstrap nav to current page and to child pages too.
I found some answers by googling, but I didn't really get very far.
My function.php looks like this:
<?php
remove_filter('the_content', 'wpautop');
remove_filter('the_excerpt', 'wpautop');
add_filter('nav_menu_css_class', 'special_nav_class', 10, 2);
function special_nav_class($classes, $item){
if( in_array('current_page_parent', $classes) ){
$classes[] = 'active ';
}
return $classes;
}
?>
I'm not really sure what I should try. I find the whole WordPress thing very strange.
There seems to be no current_page_item class here.. should I do anything special to enable it?
li.current_page_parent a {} won't work, nor will setting class="<?php if (is_page('name-of-page')) echo 'active'; ?>" inside a tags... goddamn WordPress...
Never mind.. I'm just bit slow.... I put class="<?php if (is_page('why')) echo 'active'; ?>" inside every li element.

Answer 1

If anyone ends up here:
You should check if the page is active or the page is child of another page
<li class="<?php if (is_page('offices')) echo 'active'; ?>">Offices</li>
Checks if page is "offices" and
<li class="<?php if (is_page_child(143)) echo 'active'; ?> echo 'active'; ?>">
Checks if page is child page of page with id "143" and then echoes "active" inside class=" "