Translation:That boy is marrying my young cousin.
Not so long ago, I have read in another discussion that there was one instance in the tips and notes where a verb was incorrectly allocated to genitive section, while it takes the accusative. Unfortunately, I don't remember in which tips and notes section it was (probably teaching genitive). It was definitely a reflexive verb and I think it was the "brát si" that you're referring to here (this issue with cases might as well be fixed by now, I'm not sure).
Take it as a thought where you might have copied it from.
On the other hand, having so few people working on the whole course and Czech being so grammatically diverse, it's pretty impressive how well the course is constructed and how every detail is taken into consideration and is well explained with every word having its purpose in the definitions. :-)
Dear Jamie and Vladimir. I like this discussion and more particularly your extremely kind efforts to explain! But I still would like to understand this some better. Does that mean that without preposition, brát si gets always accusative? And in case the sentence is composed with a preposition, does it take genitive only used with "od" or can it be genitive with other prepositions too? Sorry being scrupulous by trying to understand, but I can't cope with unclear issues. I like studying Czech so much :-) Thanks both of you!
It is hard to write rules that work always. In natural languages you can find exceptions to all rules :)
Without a preposition it is always accusative, yes. But in bookish texts it can be negatove or partitive genitive. "brát si peněz" is then the same as "brát si peníze". Don't worry sbout it if you don't know what a partitive genitive is.
With preposition with the meaning "from" it can be "od" or "z" or "ze", in older orthography olso "s" and "se" (meaning the same as "z"/"ze").
But you can also take something somewhere, so also "na, k, do, v, před, za, pod, nad,..." ... all possible locations. The cases then follow the rules of the prepositions and will be accusative where there is a choice between accusative and locative.
There are also some more meanings of brát (si) in the dictionary which are often quite localized. Let's ignore them.
"Getting married to" is also accepted. The use of "wedding" in the sense of "marrying / getting married to" would be very unusual in present-day speech. It is most often used now to refer to the marriage ceremony itself and/or the celebration that follows it: "I'm going to a wedding on Saturday."
Well obviously I wasn't intending to suggest that it was anywhere near as common as 'to get married'! But as you can see - a whopping 0.00000005% of the people still use it. Though that might actually just be me... I shall just have to see what I can do to increase its usage in common parlance!!