I might be missing the boat here, but "Ägypterinen" would match both if statements, meaning at the end you would have $g = "f", $q = "plural", which I can only presume is the intent of the exercise.

Like you pointed out, though, this is just a bunch of if statements, and goes one way only.

However, you really haven't given any idea as to where you're going with this, other than some loose hints. Are you trying to write a parser for German, or a sub-set of German, or a parser that can work on any language, including German. The scope is important.

First, I would try and express the rules in Perl using some sort of data structure. In many cases, the design of your algorithm can come straight from your data design. In others, it is the other way around. Either way, you have to start somewhere, so if you have no idea how to implement it, at least you can describe it.