unicode characters do not appear in gnome terminal for vim airline
Solution 1:
I've uploaded a Unicode test file which you should download and then cat in your terminal.
E.g.:
cat ~/Downloads/Unicode-sample.txt and then use Shift+PgUp and Shift+PgDn in the terminal to verify whether all characters display correctly.
If you get the same results in your terminal as opening the original source file in your browser, your font is fine; otherwise, it's a dodgy font: use a different one. (I use "Envy Code R")
And once the terminal is fine, all applications running in the terminal will be fine as well!