I have noticed that the multilang spans do not work as expected in course titles in the latest version of the theme boost in moodle 3.2. The problem is when I add the span tags, the title in both languages are displayed at the same time.
I added following code in Full course name field.
<span lang="en" class="multilang">Biology</span><span lang="ar" class="multilang">مادة الاحياء</span>
I have as already stated enabled the multi-lang filter for both “Content and headings”.
Source: Stack Overflow