Standard method (if some language variables are already registered in the controller)

1.Add a new variable to your controller /catalog/controller/...

$data['new_variable'] = $this->language->get('new_variable');

2.In the language file /catalog/language/... add

$_['new_variable']          = 'New lang variable';

3.In tpl file /catalog/view/theme/your_theme/template/... in the required place add

<?php echo $new_variable; ?>

For Page types that don't have a language controller. Using the example of the main page (Home)

1) in /catalog/controller/common/home.php after public function index() { add

$this->load->language('common/home');

$data['contact_title'] = $this->language->get('contact_title');

2) in /catalog/language/uk-ua/common create home.php file and add

<?php
// Text
$_['contact_title']          = 'Контакти';

we do the same for all languages

3) in /catalog/view/theme/yourtheme/template/common/home.tpl add it to the desired place

<?php echo $contact_title; ?>