So. Thank you to everyone for the patience.
There are still some To Do things. I will summarize the changes:

+ SQLite autogenerated in the Plugins directory of the server.

+ Fixed the console exception when the active mission is kill a chicken and you (or other things) kill a no chicken Entity (ups...)

Know issues / To do things:

- Add English, French, ... in to the .yml of the plugin

- Posibility of choose a world where the plugin will be active (in case of servers with two or more worlds)

- Villagers with no name (already generated before the activation of the plugin) wouldn't break the plugin, because it uses the UUID of the villager as track method. But in the messages of completion of a quest, their names will not appear.

- Add a "ScoreBoard" with the name of a player and the number of mission completed. Top players in the list = Players with biggest number of missions completed.

- The track method of the villagers givers of a mission is .setGlow, So, if it is used in multiplayer, you will see some villagers glowing like a twilight film (xD). The effect should dissapear when you receive the reward, but in multiplayer the effect will perdure till you are far (+- 70 blocks of distance)

- If you reload the server without ending a mission, The villager will maintain the glow effect and the database will be needed to be rebooted