How to Russify a Drupal 8 template and update the core?

Question

Drupal

Hello! Instructed to create a real estate project. The customer went through a bunch of CMS and a bunch of templates, both paid and free, but something didn’t suit him everywhere. Finally, we agreed that we need a Hostel template from Ordasoft based on Drupal 8.2.7. But here's the problem, I'm practically not familiar with this engine. But it’s good that the template distribution kit had a QuickStart Package, which I easily deployed. But everything would be fine, but I ran into several unexpected problems.
1. I wanted to immediately update to the current version, but the site "lay down" with a white screen, and did not turn on anymore. I started rolling out kernel updates gradually, but I could no longer upgrade above 8.4.8, when I upgraded to version 8.5.0, the site crashed again. At the same time, maintenance mode was enabled and the cache was cleared. What should be the sequence of versions for a successful upgrade? It was possible to update the modules one by one through the admin panel. Perhaps somehow through Composer you can painlessly update, or through Drush.
2. The second problem arose when adding Russian Localization. Multilingual modules are present, there are checkboxes on them, but they are shaded, and there is no way to turn them off. When loading Localization, the process reaches 78%, and falls out with a five-hundredth error. When entering the Chosen module, a white screen appears, and when entering the User interface translation section, it is also impossible to enter, the same white screen. Is it possible to force shutdown and reinstall Multilingual modules to return full functionality to it, and the ability to manually import localization? Obviously, the Chosen module is also somehow connected with localization.
3. I would like to say the same about the manual localization of modules. Is it possible to somehow Russify them separately from the core of the system? It just seems to be quite ordinary things, we mean updating the engine, and its localization, and so much complexity in implementation. Perhaps I'm not a very big connoisseur of CMS, but on other systems, it took three or four evenings to file the site, and then I was completely confused. Please do not throw slippers. I welcome any advice and constructive criticism. I really need help. The system is good, interesting, unusual, but unfamiliar.
PS Please do not send to other CMS ... Thanks to everyone who responds ... In advance.

Answer 1

Work with drupal 8 only through composer, installation, upgrade, removal. Then the errors can be solved in a couple of commands.
1. Install - composer create-project drupal-composer/drupal-project:8.x-dev . --no-interaction
2. In the root folder, add composer require drupal/theme_name or plugin_name
3. Update composer update 4. Then drush updb
-y and drush entity-updates
5. Clean cache drush cr the need to update the dependencies through the composer 2. Modules are translated through Languages ​​- Interface translation, if the text in the modules does not support translation of the form {{ field|t }} then you will not be able to translate the field. If only a crutch like js.