Lingua::TypoGenerator has been a great help for me in my business as it creates a good list of typo errors that are likely to be produced. Unfortunately it uses an english keyboard layout and thus missed some typos a German user might make.
For some time I have had the plan to roll my own typo generator perl module and lately came up with Lingua::DE::TypoGenerator. The name is a little bit preliminary as I have only just registered the namespace with CPAN, so perhaps if it is not accepted the name will have to be changed.

The module can be used either old-style by importing the “typos” function or in OO-style. “typos” accepts one word and will return an array of all likely typo errors including umlauts and numbers. Errors with special characters like a dot or comma are not included. If there is a need for this I can add it in later versions.

Right now all input has to come encoded in ISO-8859-1 but support for more character sets is already partly included.

If you want to give the module a try you can download it here: Lingua-DE-TypoGenerator-0.1.tar.gz