C-473/18: Judgment of the Court (Eighth Chamber) of 4 September 2019 (request for a preliminary ruling from the Finanzgericht Baden-Württemberg — Germany) — GP v Bundesagentur für Arbeit, Familienkasse Baden-Württemberg West (Reference for a preliminary ruling – Social security – Migrant workers – EU rules on the conversion of currencies – Regulation (EC) No 987/2009 – Decision No H3 of the Administrative Commission for the coordination of social security systems – Calculation of the differential supplement for family allowance, owed to a worker residing in a Member State and working in Switzerland – Determination of the reference date for the exchange rate)