Are you using the physical keyboard when typing into those boxes, or are you using the on screen keyboard?

Try both on a web page. If only on screen keyboard fails then we can assume the problem is there. Then we can try to figure out which package the keyboard lives in and reinstall it.

Also try changing your input settings under "Settings - Text input", to see if it stops whatever is triggering the error.

Does anyone know if/where word completion stores its list of words used? If that is what's broken it might help moving/renaming the file, if anyone knows where to find it.

And please make a not of what settings you change, and copies of any word list file, that way a bug report can have as much detail as possible so it can be sorted so this doesn't happen to anyone else.