After installing essentials you may want to change the language, to do so go to plugins\essentials and edit the file config.yml.
Press CTRL+F and search for "#locale: en" or just scroll down until you find the line #locale: en
Uncomment the line (remove the #) if you want your essentials in English.
So you had:
# Set the locale for all messages
# If you don't set this, the default locale of the server will be used.
# Don't forget to remove the # infront of the line
#locale: en
and now you got:
# Set the locale for all messages
# If you don't set this, the default locale of the server will be used.
# Don't forget to remove the # infront of the line
locale: en
Save and restart server
French
Spanish