Dictionaries and spell-checking
Only iOS links the keyboard and the spellcheck, OS X has never done that.  Most people find "automatic" unreliable.  To activate czech spellcheck, you should set the spell check to czech, either in system prefs/language &amp; text/text/spelling or in Edit > Spelling and Grammar > Show Spelling and Grammar.  In Pages 4 and earlier and iBooks Author, you need to set Inspector > Text > More > Language.  MS Word and some other apps do their own thing.

The app Nisus Writer has preference settings that let you link keyboard and spellcheck dictionary.