It may happen to you as it did to me to sometimes read messages with "tofu" characters in it: these boxes with numbers in it. It means they can't be displayed with the fonts installed on your machine. Before, I didn't pay much attention to it because I could still read the message, but I really got interested while working on Qowala when some messages had only this kind of characters.
TL;DR: Display most emojis on Arch Linux by installing the Noto font for emojis by Google with the following command:
sudo pacman -S noto-fonts-emoji.
In fact, when I checked the same message on Twitter's website as the one displayed on Qowala, I could see it was emojis. I could see it because it was Twitter's own emojis which were in fact images. As Twitter released its opensource library of emojis, I could integrate it in Qowala's new version currently in development and fixed this mean boxes!
Emojis fixed on Qowala 1.0!
Okay, I went a little bit out the subject, but it's because of this episode while coding for Qowala that I pay more attention to these characters. I'm using elementaryOS and Arch Linux on my computers to really have the two opposites of what is available in the Linux experience and I noticed that an email in Thunderbird on elementaryOS displayed a character that I didn't have on Arch Linux. Frustrated of not having the correct emoji, I searched how to display it on my Arch Linux. After some little research on the fontWiki of Arch Linux, I found the Noto font from Google being the right one. As it displays exactly the same emoji on my elementaryOS, I assume it is the one used by default on Ubuntu-based distributions.
I missed this clock emoji on Arch Linux
So if you want to display some emojis on your Arch linux, just install the noto-fonts-emoji package with the following command:
sudo pacman -S noto-fonts-emoji
If you have more information on which fonts are the best in terms of compatibility and numbers of glyphs, please let me know!