The language may have been german, though I'm not entirely sure.
The book was about a group of children who were selected through some test(s)/tasks they had to complete. I'd say it had a more medieval setting, definitely not modern.
The tasks were at the very beginning of the story, and they had to solve a riddle to figure out the location of an item in a city (maybe a scroll?). There was some cooperation between the participants, and they had to climb a statue to get one of the items required to pass the test.
Only a handful passed, and they were brought to a castle or so and, after another competition to determine who gets to choose first, received an amulet/pendant (probably with necklace) that they could use to summon a sort of familiar. To use it, they had to whisper the secret name they chose (or that was told to them by the familiar) when they first used the amulet/pendant. The name mustn't be known by anyone else but the user.
There was some conflict with a girl accusing the protagonist of hiding her amulet/pendant while she was taking a bath but that got resolved soon I think.
It was probably the first book in a series. Also more aimed at children/a younger audience.