No matter how good your list of words, it won't be good enough. However, it would be interesting to look at an AI approach that used the word lists along with some knowledge of grammer to implement an AI alg. I know a previous poster had said AI is a failure, but I think an AI approach may serve you well here. I'm thinking about some kind of neural network might actually do a decent job.
Between knowing that most will be German, having word lists, etc, I feel like you could put together a relatively successful neural net to guess the language of a word. Of course it won't be error free, but I bet whatever your solution is to this hum-dinger, it will contain some errors.
Good luck! This is a terrific problem and I'd love to know how you solve it.
in reply to detecting the language of a word?