As a native Icelandic speaker, I have an intuition for how to decline names -- I don't really think about it consciously. I'd assume that for most people it's just pattern matching.

Native speakers very frequently decline names in ways that are not technically perfect but sound correct enough. For example, my name (Alex) should not be declined, but people frequently use the declension pattern (Alex, Alex, Alexi, Alexar).

There's some parallel to be drawn with how the compressed trie applies patterns that it's learned to names. That's at least how I thought about it when designing the library.

They stick with the nominative case. That’s the only safe way not to butcher somebody’s name in a language like Estonian that has 14 cases. It’s infinitely easier to update copy to use only nominative than try to apply the cases automatically.