What fonts do I need to install on Ubuntu in order to see special characters (💋 for example)?
Well apparently this was a "fonts" problem for specific languages.
Visit this Wikipedia page: List of ISO 639-1 codes and check the languages that aren't working for you.
I had the same issue for the Tibetan language which were showing those squares instead of the actual character. Installing the package
fonts-tibetan-machine fixed the problems for that exact language.
sudo apt-get install fonts-tibetan-machine
So in order to fix the other languages, you need to install the necessary font package for that language.