PHP Nested functions logic error - translating functions.php with WPML

I am translating a piece of text that shows up on the checkout page with custom code that I am using. How do I correctly use nested functions in PHP?

I changed echo to a WPML recognizable function, but to no avail on the frontend.

add_action( 'woocommerce_review_order_before_submit', 'bbloomer_checkout_add_on', 9999 );

function bbloomer_checkout_add_on() {
   $product_ids = array( 14877, 14879, 15493 );
   $in_cart = false;
   foreach( WC()->cart->get_cart() as $cart_item ) {
      $product_in_cart = $cart_item['product_id'];
      if ( in_array( $product_in_cart, $product_ids ) ) {
         $in_cart = true;
         break;
      }
   }
   if ( ! $in_cart ) {
      echo '<h4><b>● Would you like to add 10/20/30 small sample vials?</b></h4>';

      function change_sm_location_search_title( $original_value ) {
    return '<h4><b>' . __('● Would you like to add 10/20/30 small sample vials?','text-domain') . '</b></h4>';
}
add_filter( 'sm-location-search-title', 'change_sm_location_search_title' );

      echo '<p><a class="button" style="width: 140px" href="?add-to-cart=1183"> €1.2 (10) </a><a class="button" style="width: 140px" href="?add-to-cart=9945"> €2.1 (20)</a><a class="button" style="width: 140px" href="?add-to-cart=9948"> €3 (30)</a></p>';
   }
}

The echo stills shows up on frontend, but new text-domain function only shows up on backend.

Solution

Filters are used to replace values. You should bring the filter function declaration outside of the main function and use apply_filters call to use the filter.

You can also use action hook instead. I suggest reading up on using hooks and filters: https://docs.presscustomizr.com/article/26-wordpress-actions-filters-and-hooks-a-guide-for-non-developers

And this answer here for a better understanding how the filter is working: https://wordpress.stackexchange.com/questions/97356/trouble-understanding-apply-filters

This should work (untested).

add_action( 'woocommerce_review_order_before_submit', 'bbloomer_checkout_add_on', 9999 );

    function bbloomer_checkout_add_on() {
       $product_ids = array( 14877, 14879, 15493 );
       $in_cart = false;
       foreach( WC()->cart->get_cart() as $cart_item ) {
          $product_in_cart = $cart_item['product_id'];
          if ( in_array( $product_in_cart, $product_ids ) ) {
             $in_cart = true;
             break;
          }
       }
       if ( ! $in_cart ) {
          echo apply_filters('sm-location-search-title', 'Would you like to add 10/20/30 small sample vials?');
          echo '<p><a class="button" style="width: 140px" href="?add-to-cart=1183"> €1.2 (10) </a><a class="button" style="width: 140px" href="?add-to-cart=9945"> €2.1 (20)</a><a class="button" style="width: 140px" href="?add-to-cart=9948"> €3 (30)</a></p>';
       }
    }   
    function change_sm_location_search_title( $original_value ) {
      return '<h4><b>' . __($original_value,'text-domain') . '</b></h4>';
    }  
    add_filter( 'sm-location-search-title', 'change_sm_location_search_title');