It's a triton marbré., Triturus marmoratus. Found in France and Spain. Found in hedges, heathland, wooded areas, and semi nocturnal. You could release it anywhere where it won't instantly be eaten by something larger although salamanders are reputedly poisonous or at any rate unpleasant to eat. We get fire salamanders round us in Finistere. We may well get these but I have never seen one in the garden.