

I’ve never used xfce, I used Gnome previously and currently KDE Plasma, and I liked fcitx for both. However I had a bug with Anki where it wasn’t able to change language inputs with fcitx, so I had to switch to iBus. Both work fine, although I liked that Fcitx showed the conversion preview without having to hit tab, while iBus does.
The squares is probably a font issue, this article might help. You can easily switch input for both apps and set up your own shortcut combo.
Sorry, I have dummy noob moments 😔
I use KDE Plasma