I am now on level 25 with 18000 points. When do I reach level 26?
How did you get to level 25? You normally need 30,000 XP to reach that level. Just checked, you have 48,000 XP, not 18,000.
There is no level 26, although you can continue earning XP.
To add on, all languages currently have 25 Levels. I believe they meant 18,000 XP on Level 25, not overall.
It's just being odd. There's no Level 26, even if you receive E-mails from it. There'll be glitches where the site actually thinks you got to Level 26 and shows a Badge, but it's not permanent.