I have not completed the game so far ( up to now just testing things...), But i have a question: how is the whole fulvano vojage implemented? Nobody speaked about it

All the locations are there - but there isn't a connected 'Fulvano's voyage' quest. Without giving too much away, some of the area's are linked by side quests. If you go back to the fig information about the voyage you should be able to find the locations without a problem. 

 

I didn't actually find any references in game about Fulvano.

Now that you mention it, Fulvano's name seems to have been completely scrapped from the project. But there is a guy who asks you to explore a bunch of islands.

Fulvano's voyage was changed to map uncharted Islands quest. Quest is given to you in Neketaka by some cartogprapher.
Areas are well desigend but they are quite small, in some cases It's 1 building with 1 room and 1 fight. Some are  little bit bigger, but in general they feel underwhelming.
They one of the weaker points of the game and can'ts stand their ground compared to Endless paths.