Theme settings are not translatable

@Tanushree Gupta, thanks for your contribution. However, your work does focus on translating the strings, already hard coded in the slider.html.twig file. It won't work with the "slider_code" variable.

I've added a simple "trans" function in the last part of the array. Can you check this one too?

I'm also uploading my commit as a patch file, in order to use it in my composer.json file, until it merges into stable branch.

Unfortunately, user interface translation doesn't accept translating HTML tags. I'm changing the issue's status.