Drupal 8.x

I have been trying to make the multilingual module in a 8.5.3 core Drupal site work. I have two languages in the site, English and Greek (Greek is the default language) and have translated a Story item, initially in Greek language, into English and the problem I have is that both translations of the Story article are displayed on the front page when I either click the 'English' link of the language switcher, or the 'Greek' link. 

I would appreciate any tips.

My site, which is essentially "read only," randomly fails to load, with the following message:

The website encountered an unexpected error. Please try again later.
Error: Unsupported operand types in Drupal\views\Element\View::preRenderViewElement() (line 49 of core/modules/views/src/Element/View.php).

Here are the environment specifics: 
  Hosting environment: Pantheon (Personal service level)
  Drupal: 8.5.3
  PHP: 7.1.17
  DB System Version: 5.5.5-10.0.23-MariaDB-log

Hello,

For the past couple of weeks, I've been trying to upgrade to the latest Drupal. I've tried different ways but still got no further. Here are my current settings:

Current Version:
Drupal 8.3.7
php 5.6
Drush 8
Composer 1.4.1

Goal:
Drupal 8.5.3
php 7.2
Drush 9
Latest Composer

How I usually upgrade:
Manually take backup of /core and save it. Replace old core with new core directory. Then run update.php from site. Unfortunately, it doesn't work for this process.

I'm extremely rusty on doing any php coding, and I'm not quite sure how to reference fields from within a custom token (Drupal 8)

I think I might have it, but the token didn't appear in my pop-up of options after enabling the module. Also, I'm not sure if I did the if-else statement correct.. or maybe somebody knows a better way. (for extra clarification: It's a simple token to create a URL-safe replacement for a multiplication sign, so I can use that token in my pathauto patterns for the relevant node.)

Here's what I got in the .yml: