Ciao Luca,
I did some searching round and found some information for you just in case you did not know this already.
Here is a document which explains how to add Course names etc.
https://docs.moodle.org/33/en/Multi-language_content_filter
The way the Courses are displayed on the Frontpage in Klass theme you need to use the Moodle <span lang="EN" class="multilang">Course name</span> and have the Plugin > Multi Language Filter enabled and not the Plugins you are using, as that uses a different code altogether.
However even with just the options in Moodle the Course title on the frontpage course list as duel languages which is wrong, so this is a Theme problem. I will see if I can replicate this in my Moodle test site?
I have also found a coding error in the KLASS theme which I want to try and fix for you.
Mary