In your theme, in model_patches.rb, you can override the method like :
title =~ /^(FOI|Freedom of Information)\s*requests?$/i
You can then replace the regular expression with something that works better in your context.
As you can see, there's an "OR" conditional, so we match:
* FOI requests
* Freedom of Information requests
I think you'd change the regexp to something like:
title =~ /^zahtjev.*(PPI|pravo zna pristup informacijama)?$/i
FYI, the trailing `/i` makes the match case insensitive.
I've created an issue  to note that this isn't easily translatable.
 I think this is what you need, given InfoRequest::TitleValidation is a module not a class. If it doesn't work we'll take a closer look.