With great help from shoover and JPmiaou in the other Q&A about the marriage between Marie Emma Kafka-Somfai and Dr. Karl Ritter von Taussig I found out that both husband and wife were adopted but both of them only for a limited amount of time.
Marie Emma was adopted by Ferenc Somfai as can be seen in the additional notes to her first marriage to Josef Wregg (in Vienna, therefore in German):
„Nach einer an das k.k. Ministerium des Innern getätigten Mitteilung des Königl(ich) ungar(ischen) Justizminist(eriums) vom 11. Oktober 1910 Z(iffer) 2277/1910 ist die am 15. September 1879 in Brünn geborene, in Wien wohnhafte Maria Emma Kafka, Ehegattin des Josef Wregg, von dem in Budapest wohnhaften ungarischen Staatsangehörigen Franz Somfai adoptiert worden. Vermöge dieser Adoption hat der Geburtsfamilienname der Adoptierten in Hinkunft „Kafka-Somfai“ zu lauten. Erlass des k.k. Ministeriums des Innern vom 4. November 1910, Z(iffer) 40160.“
Which roughly translates to:
"After a message to the k.k. Ministry of the Interior, issued by the Royal Hungarian Ministry of Justice on October 11, 1910, No. 2277/1910, has Maria Emma Kafka, born in Brno on September 15, 1879 and living in Vienna, wife of Josef Wregg, been adopted by the Hungarian citizen Franz Somfai who lives in Budapest. As a result of this adoption, the birth surname of the adopted woman should be "Kafka-Somfai" in the future. Decree of the k.k. Ministry of the Interior from November 4, 1910, No. 40160."
But there is also a later note stating:
„Nach einer an das k.k. Ministerium des Innern getätigten Mitteilung des königl(ich) ungarischen Justizministeriums vom 29. April 1911 Z(iffer) 544 ist der zwischen Maria Emma Kafka, Ehegattin des Josef Wregg und Franz Somfai geschlossene Adoptionsvertrag aufgelöst worden. – Demzufolge wird die Adoptierte in Hinkunft ihren früheren Familiennamen zu führen haben.“
"After a message to the k.k. Ministry of the Interior issued by the Royal Hungarian Ministry of Justice on April 29, 1911, No. 544, the adoption agreement between Maria Emma Kafka, wife of Josef Wregg, and Franz Somfai has been dissolved. As a result, the adopted woman will have her former surname in the future."
So we see that she was only adopted between about October 1910 and April 1911. Only for a rather short time.
With Karl it's the same case, he was adopted by János Német in December 1910 and in February 1912 the adoption was annulled.
A later added note to his birth register entry:
Nach einer an das k.k. Ministerium des Innern gelangten Mitteilung des kgl. ungarischen Justizministeriums vom 24.12.1910 […] ist der am 16.02.1878 geborene und in Wien wohnhafte Karl Ritter von Taussig von dem in Budapest wohnhaften ungarischen Staatsangehörigen Johann Német adoptiert worden.
According to a message from the Royal Hungarian Ministry of Justice of December 24, 1910 […], Karl Ritter von Taussig, who was born in Vienna on February 16, 1878, was adopted by the Hungarian citizen Johann Német, who lives in Budapest.
And from a later added note from the entry of his marriage to Marie Emma:
The adoption contract between Sir Károly Taussig and János Német having been dissolved, the herein-entered groom is obliged and entitled to use the family name Taussig alone in the future. […] February 28, 1912
(Translation of Hungarian original by JPmiaou in the other thread.)
I am assuming that there was a legal reason for getting adopted temporarily. Maybe to be able to get a civil marriage in Hungary which otherwise wouldn't have been possible. I wonder whether it played a role that the bride was divorced before their marriage and that both were of different faiths.
Am I correct and this was common widespread practice under the aforementioned circumstances and is something which perhaps can be useful for genealogical research nowadays and if so then how? (Adoption registry?)
Or in short: Can someone tell me what happened here?