Many people would like to spell-check documents written in mixed languages (such as English and German). There are work-arounds involving concatenating dictionaries, but this is a mess.
It would be nice to have a multiple-language override for the dictionary selection, say, something like
This would mean to look each word up in the German dictionary first, then in the English. If the word is not found in either, a list of alternatives from the two languages could be presented.
A little more elaborate: Formats such as HTML can specify the language of different parts of a document. It would be cool if aspell could check spelling in the correct language for each part.
I have often needed this kind of functionality in several programs, and see that many other people want it as well.
Here are people asking for something similar:
Here is a guy who rigged something up for Psi:
Here are instructions on how to concatenate dictionaries: