[Doitsu]

Originally Posted by geotadams

That was my first thought too, unfortunately when I was attempting to do that it was taking hours on end and stopping at 40% so I had to give up.

Have you tried the KindleUnpack Calibre plugin?
It typically takes less than a minute to unpack a .mobi dictionary. Unfortunately, the plugin can't reverse-engineer the inflections of all dictionaries. The Duden is one of those books. Try unpacking one of the bilingual Oxford dictionaries instead.

Originally Posted by geotadams

Is there a way for the average user to implement what Duden was able to do, or am I going to just have to put all the possible definitions in one entry?

You'll have to define inflections for each entry. Here's an example from the Kindle Publishing Guidelines.

<idx:entry name="english" scriptable="yes" spell="yes">
    <idx:short><a id="1"></a>
        <idx:orth value="aardvark">
            <b>aard•vark</b>
            <idx:infl>
                <idx:iform value="aardvarks"></idx:iform>
                <idx:iform value="aardvark’s"></idx:iform>
                <idx:iform value="aardvarks’"></idx:iform>
            </idx:infl>
        </idx:orth>
        <p> A nocturnal burrowing mammal native to sub-Saharan Africa that feeds exclusively on ants and termites.</p>
    </idx:short>
</idx:entry>