no and yes. no because the button text is determined by the language locale of the system being run on. yes because it is possible via means to hack the messagebox and alter the text but that can (and has been known to cause other issues).
so really, the safest way is to create your own messagebox (using nswindows i believe) which allows you to set the text as needed. it's probably not elegant but there is no version of the hack still available (i used to provide a replacement messagebox plug-in which used the hack method but lost the source code and the prior compile didn't work with newer NSIS and Windows versions). or you need to find someone willing to re-create the hack for you (i'm not able to).
Thanks, I told my Product Owner to create a new Story to implement own message boxed if this is really important ;-)
But btw. is there a reason, why everything is translatable but the buttons in message boxes are not?