Install libgtkspell3-3-0 by entering the following commands in the terminal:
sudo apt update sudo apt install libgtkspell3-3-0
Description:
spell-checking addon for GTK+'s TextView widget
GtkSpell provides Microsoft Word/OS X-style highlighting of misspelled words in a GtkTextView widget. Right-clicking a misspelled word pops up a menu of suggested replacements.
Homepage: http://gtkspell.sourceforge.net/
Version: 3.0.9-2
Section: universe/libs