This feature is no longer supported or relevant because browsers now have spellchecking, and that's where it should be handled.
SpellcheckingTiki contains an optional spellchecking ability that uses its own dictionary. When entering wiki text in specific features, Tiki can automatically identify misspelled words and offer suggestions.
The language-specific dictionary used by the spellchecker is an additional database table that can be downloaded from Sourceforge and added to your database.
Q: Why does spellcheck flag all capitalized words as incorrect?
A: Because it has been broken for a long time. See this post from 2007.