I'm not sure - particularly on this site - that it can be assumed that all English speakers assume that if a name ends in 'a' it's feminine.
Luka and
Luca (pronounced Loo-ka) are/have been used as diminutives of a number of girl's names over time - including
Lucretia, Lukina, Lukiia and Lukardis. I would imagine the names could also work for
Lucrece,
Ludovica and
Ludwika.
I'm not sure when diminutives become 'legitimately' considered usable in their own right - but both
Luka and
Luca have been used as stand-alone girl's names (outside of Hungary, and (interestingly) most often in Europe) for some time - even if they have never reached 'top ten' or 'top 100' status.
In addition, they are also stand-alone names in their own right, without having developed as diminutives (one of the Period Russian Name links on this site lists
Luka as most likely being a feminine version of Luk;
Luka is the Hawaiian version of
Ruth etc)
I appreciate that must come across as odd in Croatia - where
Luka has been the most popular boy's name for so long - but to dismiss the use of
Luca and
Luka on girls as somehow representing 'English ignorance' isn't quite right.
(and had to add -
Noah is a girl's name as well :)