Diamonds is the premium money of the server. You can earn them by 6 ways :

• Donation : Donation can be make by paypal or visa card, see here

• Feed the server with skins : On the website, in your char account, you can charge your character's skin (screenshot and paint) if no skin is available. it may exists infinite combinaison of skins.

• Sell your stuff on the marketplace : You can sell your stuff on the website, no control on the price. 2 types of selling : simple sell or bid. Bid allow players to bid on your stuff for the time you want. See here
• Participate on the forum : If you are active on the forum, you can win each week a certain amount of diamonds. See here
• Report bugs : You can win diamonds by reporting bugs on the server and the website. the more serious the bug, the greater the reward. You can report bugs by contact : l2savage.contact@gmail.com
• Farming border outpost zone : This is a PVP zone with high monster so it'll not be easy.