Re levels

When I re-level with a wizard: do I lost spells i've lerned from the scrolls??
And Is it possible to re-level again after using the scale?

You'll get a second set of scales at 20th level, so relevelling again shouldn't be a problem. As far as your spellbook, yeah, I'm pretty sure you lose all your known spells when you lose the level needed to know them. Of course, that doesn't mean you can't scribe yourself a bunch of scrolls before you use the scales

Spells learned from Scrolls will remain in your spells known list even when you re-level.

Only spells chosen at levelup will be lost, and they can of course be chosen again when you level back up.

Oh, neat!

Yeah, I made good use of this when I was relevelling Crid. I bought a megaton of scrolls of spells I had chosen at levelup, then I knocked myself down to level 1, levelled up to where I could learn the scrolls, and then learned them all. There are still a handful of spells I dont have on Crid, even after levelling back up to 40, but Im confident I have the really good ones at least.

The scroll thing sort of makes up for the balance issue with sorcerors being able to use metamagic spontaneously without increasing cast time. Wizards get to know just about every spell if they want to... now if only we could memorize them all...

Relevelling is also a handy trick for a wizard to get the newest spells (illusionary spell/object/monkster, Force Cage), as well, since those scrolls don't have a scroll to them yet.