Earning new spell levels in Dungeonslayers

When a mage earns a level, I don’t quite understand the spell learning mechanics.

Applicable rule:

LEARNING NEW SPELLS

When a spellcaster reaches a higher level,
he can learn new spells. This doesn’t cost any learning
points. Instead the spell must already be in possession of the
character. If not he must try to find new spells during adventuring
(or purchase them in a library for example). For each new
level, a spellcaster can learn new spells until the sum of the spells’
levels is equal to the character’s new level.

I’m not sure the player earns just one spell level (e.g. a 5 level wizard could learn a total of 1+1+1+1+1=5 spell levels) or earns a number of spells levels equal to its new experience level (i.e. same wizard could learn a total of 1+2+3+4+5=15).

The former seems a bit underpowered and unflexible, while the later is clearly overpowered IMO.

English is not my first language so maybe the meaning as written is not as ambiguous as it looks to me, or maybe is just a translation problem (it’s a german game).

Any insight is welcome.