Hi,

I've been looking through en_US.lang and config.yml and found a few errors. Most are very minor errors or don't fit into uniformity of the plugin. I also looked at the achievements list (/mh kills) and found a few that didn't sound quite right.

Note that I don't speak English fluently. Make sure my suggestions are proper language =)

en_US.lang

12:
achievements.fancypants.description=Complete a kill with a fully enchanted set of diamond armor and sword.
#Rephrased

16:
achievements.huntbegins.description=Make your first hunt. There are more achievements to get for killing mobs in interesting and unique ways.
#Rephrased

35:
achievements.itsmagic.name=It's Magic!
#Forgot the ' character

39
achievements.master-sniper.description=Snipe a mob from over 40 blocks away while in a moving vehicle or on a moving horse.
#Added word 'from'

149:
mobhunting.commands.head.you_got_a_head=You got the head of a ${mobname}
#Replaced 'a' with 'the'

187:
mobhunting.commands.npc.unknown_rank=Rank (&b${rank}&f)must be greater than 0 and less than 26
#Fixed typo

207:
mobhunting.commands.top.invalid-number=Count must be a whole number within the range of 1-100
#Replaced 'with' with 'within'

Open for debate:
86:
mobhunting.bounty.playeriswanted=There is a bounty on ${playername}, go get him!

87:
mobhunting.bounty.randombounty=A Random Bounty (${prize}) was put on ${playername}, go get him!

116:
mobhunting.commands.bounty.description=Put a bounty on your enemy and get him killed.

Is assuming gender ok? I doubt anyone will care, though. =)

config.yml

47:
elder-guardian-cmd-desc: You got an Elder Guardian skull and an Iron ingot.
#Fixed grammar ('a' should be 'an')

52:
enderman-cmd-desc: You got an Enderman skull and a Gold ingot.
#Fixed grammar ('a' should be 'an')

57:
endermite-cmd-desc: You got an Endermite skull and an Iron ingot.
#Fixed grammar ('a' should be 'an')

67:
giant-cmd-desc: You got a Giant head and an Iron Ingot.
#Replaced 'iron' with 'Iron'

72:
iron-golem-cmd-desc: You got an Iron Golem skull and 4 Iron ingots.
#Added plural to the word ingot.

87:
killerrabbit-cmd-desc: You got a Killer Rabbit skull and an Iron Ingot.
#Added missing 'a' and replaced 'iron' with 'Iron'

121:
silverfish-cmd-desc: You got a Silverfish head and an Iron ingot.
#Replaced 'SilverFish' with 'Silverfish' and 'iron' with 'Iron'

126
skeleton-cmd-desc: You got a Skeleton skull and one Lapis Lazuli.
#Replaced '1' with 'a' and '1' with 'one'

146:
vex-cmd-desc: You got a Vex skull and a Gold ingot.
#Fixed grammar ('an' should be 'a')

151:
witch-cmd-desc: You got a Witch skull and a Gold ingot.
#Fixed grammar ('an' should be 'a')

156:
wither-skeleton-cmd-desc: You got a Wither Skeleton skull and a Gold ingot.
#Replaced '1' with 'a' and '1' with 'a'

177:
enderdragon-cmd-desc: You got an Enderdragon skull and ten Diamonds.
#Fixed grammar ('a' should be 'an') and replaced numbers with letters

193:
butcher-cmd-desc: You got a Butcher skull
#Replaced 'Skull' with 'skull'. Cosmetic change because small s in the word skull has been used so far in the config file

198:
cartographer-cmd-desc: You got a Cartographer skull
#Replaced 'Skull' with 'skull'

203:
evoker-cmd-desc: You got an Evoker skull and an Iron ingot.
#Fixed grammar ('a' should be 'an')

208:
farmer-cmd-desc: You got a Farmer skull
#Replaced 'Skull' with 'skull'

218:
librarian-cmd-desc: You got a Librarian skull
#Replaced 'Skull' with 'skull'

223:
nitwit-cmd-desc: You got a Nitwit skull
#Replaced 'Skull' with 'skull'

228:
priest-cmd-desc: You got a Priest skull
#Replaced 'Skull' with 'skull'

233:
villager-cmd-desc: You got a Villager Skull
#Replaced 'Skull' with 'skull'

238:
vindicator-cmd-desc: You got a Vindicator skull and a Gold ingot.
#Fixed grammar ('an' should be 'a')

EVERY PASSIVE MOB - Replace 'Skull' with 'skull'

296:
ocelot-cmd-desc: 'You got an Ocelot skull'
#Added description

350:
rawfish-cmd-desc: You got the head of a Raw Fish
#Replaced 'a' with 'the'

355:
rawsalmon-cmd-desc: You got the head of a Raw Salmon
#Replaced 'a' with 'the'

360;
pufferfish-cmd-desc: You got the head of a Pufferfish
#Replaced 'a' with 'the'

365:
clownfish-cmd-desc: You got the head of a Clownfish
#Replaced 'a' with 'the'

446:
itsmagic-cmd-desc: Enjoy your Gold Ingot
#Fixed typo

449:
fancypants-cmd-desc: Enjoy your Gold Ingot
#Fixed typo and plural error

452:
master-sniper-cmd-desc: Enjoy your Gold Ingot
#Fixed typo and plural error

455:
justintime-cmd-desc: Enjoy your Gold Ingot
#Fixed typo and plural error

Achievement mob names in plural

Ender Dragons
Mushroom Cows
Endermen
Sheep
Skeleton Horses
Silverfish
Pufferfish
Raw Salmon
Wolves
Raw Fish
Clownfish

I think a fixed this in newest snapshot, but please remember that I dont change your lang file when it is generated. So you will have to delete the lang file and restart the server to see the changes.

Fixed in v4.9.3