Jep u heared right, Your config design is creation errros on older Spigot Version (lower then 1.9.x - so all 1.8.x and the firsts 1.9.x Versions)

read this Spigot post here
https://www.spigotmc.org/threads/fastcraft.133803/page-34#post-2702869
on this page a user had this problem, first i didnt understand what he wanted, or why he was posting this. then i tested it with different Spigot Versions, so see how long this error of wong config converstion exists. i crated on the spigotsite a little fix for him. For this i replaced your whole config.yml if a working one in the jarfile. i was suppriced that all "#infos" from my config got removed on creation, but ok this may is how config files are created in 1.8....
But ok, even if the # Infos are not inside the created config.yml, this "new" config.yml works for the old Spigot versions.

So may u have an idea for further updated to rethink about the creation of config.yml? <3
by the way - Fastcraft+ is this the best plugin X-D

Thanks for looking into it for me!

This has been an issue for a few people, but I've never figured out it was the version of spigot.

I'll work on a fix when I get around to it. I've been really busy with schoolwork, job searching, and a hand injury. I'll be thinking of a good solution in the meantime :)

The main problem is that unicode characters are being saved to the .yml file as escape characters.

For instance:
# Ti\u1ebfng Vi\u1ec7t (VI), Polskie (PL)
Instead of:
# Tiếng Việt (VI), Polskie (PL)

Here are some places where this may be happening:
https://github.com/BenWoodworth/FastCraft/blob/v0/dev/src/main/java/co/kepler/fastcraftplus/util/BukkitUtil.java#L112
https://github.com/BenWoodworth/FastCraft/blob/v0/dev/src/main/java/co/kepler/fastcraftplus/util/BukkitUtil.java#L84