Incompatible with dieresis ????ü

I tried out the plugin and it is (would be) very useful. However as soon as I use a dieresis (????ü) the whole content of my blog posts disappears. If this error is general, this means lots of people won‘t be able to use it, since their blog languages contain dieresis. Are other users experiencing the same issue? And (how) can it be solved? Thanks a lot.