Drupal 8.x

When I install a module, the following information is displayed

have Anybody know how to fix it？

thankyou

The website encountered an unexpected error. Please try again later.
ReflectionException: Class Drupal\ms_core\EventSubscriber\InitSubscriber does not exist in ReflectionClass->__construct() (line 30 of /Applications/MAMP/htdocs/drupal-8.8.5/core/lib/Drupal/Core/DependencyInjection/Compiler/RegisterEventSubscribersPass.php).

I have a website: https://h5pstudio.ecampusontario.ca/ I have enabled multilingual modules for the site. 

I have an issue that when i switch to the french site the Subject field are in Still in default language. i have translated the taxonomoies but it is not showing in the views table. You can see here : https://h5pstudio.ecampusontario.ca/fr 

I would like to create a demo site where people can use a theme selector to experience different themes.  I've looked into different possibilities (role based theme switcher, domain based, taxonomy based) and haven't completely given up on trying to use those.  I also tried assigning the theme management permission to a specific role but apparently managing themes requires the account be marked specifically as an administrator. Is there anything else I can try to accomplish this goal?

Hello :)

How to add a class on all form in my theme. 

I want to add on all input type text a class for exemple form-input-text.

Hello all,

I've built a site on local DEV server starting from droopler distribution installed with Acquia Dev Desktop. Once ready, I split the deployment into several steps:

1. Rebuild a new local DEV site starting from the clean Drupal Core and building-up the useful to me part of the distribution. The goal was to be in control of different aspects related to modules used, config, future update etc.

This was a nightmare...