Hi,
In the file variable.php located in neighborhood/woocommerce/single-product/add-to-cart/ find the line 80 (the code below)
<button type="submit" data-product_id="<?php echo $product->id; ?>" data-quantity="1" data-loading_text="<?php echo $loading_text; ?>" data-added_text="<?php echo $added_text; ?>" class="add_to_cart_button button alt"><?php echo apply_filters('sf_add_to_cart_icon', '<i class="sf-icon-add-to-cart"></i>'); ?><span><?php echo $product->single_add_to_cart_text(); ?></span></button>
and replace it by this one
<button type="submit" data-product_id="<?php echo $product->id; ?>" data-quantity="1" data-loading_text="<?php echo $loading_text; ?>" data-added_text="<?php echo $added_text; ?>" class="add_to_cart_button button alt"><?php echo apply_filters('sf_add_to_cart_icon', '<i class="fa-plus"></i> '); ?><span><?php echo apply_filters('single_add_to_cart_text', __("Add to shopping bag", "swiftframework"), $product->product_type); ?></span></button>
I tested in my installation and it worked.
-Rui