Case C-356/19: Judgment of the Court (Eighth Chamber) of 3 September 2020 (request for a preliminary ruling from the Sąd Rejonowy dla m. st. Warszawy w Warszawie — Poland) — Delfly sp. z o.o. v Smartwings Poland sp. z o.o., formerly Travel Service Polska sp. z o.o. (Reference for a preliminary ruling — Air transport — Regulation (EC) No 261/2004 — Article 7 — Right to compensation in the event of delay or cancellation of a flight — Compensation procedure — Claim expressed in national currency — National provision prohibiting the creditor from choosing the currency)