> Furthermore, spell-checks usually seem to be designed for languages like English with only a limited number of flections. English only has singular and plural, but in German, the ending of a word can be bent in much more ways

Oh, and I always say German works still great. In Finnish words have many 100s of different endings (several concatenated + combinatorics explain how this is possible) and predictive inputs just don't work. Probably it could be improved with massive semantic support, I am not an expert in that field.