This was the consumer protection board of the state NRW suing the Media Markt E-Business GmbH.
This current ruling is just the Oberlandesgericht München (Munich Higher Regional Court, abbr. OLG) keeping up the ruling from previous instance (OLG München, 6 U 3815/17 and LG München I, 33 O 20488/16). Mediamarkt is still allowed to ask for a revision, but is not allowed to escalate to a higher instance.
The specific case was Mediamarkt offering a Samsung Galaxy S6 for 499€ in August 2016. While ordering it would tell you multiple times that you would get one as soon as it's available, but wouldn't specify a date.
This is against the law (§ 312d Abs. 1 S. 1 BGB, Art. 246a § 1 Abs. 1 S. 1 Nr. 7 EGBGB), since soon can be whatever. The retailer has to name a generous last date. Per the court ruling this is to allow the (potential already paying) consumer to press charges in cases where it takes arbitrarily long.
I'm not a lawyer, and while I try my best to translate i can't guarantee for it to be 100% correct). Here are the laws in question:
§ 312d Abs. 1 S. 1 BGB
§ 312 Informationspflichten
(1) 1Bei außerhalb von Geschäftsräumen geschlossenen Verträgen und bei Fernabsatzverträgen ist der Unternehmer verpflichtet, den Verbraucher nach Maßgabe des Artikels 246a des Einführungsgesetzes zum Bürgerlichen Gesetzbuche zu informieren. 2Die in Erfüllung dieser Pflicht gemachten Angaben des Unternehmers werden Inhalt des Vertrags, es sei denn, die Vertragsparteien haben ausdrücklich etwas anderes vereinbart.
translated:
§ 312 Duty to provide information
(1) 1In the case of contracts concluded outside business premises and distance contracts, the entrepreneur is obliged to inform the consumer in accordance to Article 246a of the Introductory Act to the German Civil Code. 2The information provided by the Contractor in fulfillment of this obligation shall become part of the contract, unless the contracting parties have expressly agreed otherwise.
Art. 246a § 1 Abs. 1 S. 1 Nr. 7 EGBGB
§ 1 Informationspflichten
(1) Der Unternehmer ist nach § 312d Absatz 1 des Bürgerlichen Gesetzbuchs verpflichtet, dem Verbraucher folgende Informationen zur Verfügung zu stellen:
7. die Zahlungs-, Liefer- und Leistungsbedingungen, den Termin, bis zu dem der Unternehmer die Waren liefern oder die Dienstleistung erbringen muss, und gegebenenfalls das Verfahren des Unternehmers zum Umgang mit Beschwerden,
I picked 7 in particular because it's the one referred to in the ruling and the entire law is quite long. Translated:
§1 Duty to provide information
(1) According to § 312d paragraph 1 of the German Civil Code, the entrepreneur is obliged to provide the consumer with the following information:
7. the terms of payment, delivery and service, the date by which the entrepreneur must deliver the goods or service and, where appropriate, the procedure followed by the entrepreneur to deal with complaints,
Sources (in German):
