To spell check in QuarkXPress using a specific language dictionary is very easy. Most spell check solutions in QuarkXPress pick the language set on the text to pick the language dictionary for checking spellings. When you install QuarkXPress then the default language set in the character style sheet is one that is native to that machine. For example default text language will be US English if you installed and activated QuarkXPress in USA. If you installed and activated QuarkXPress in the UK then the default language on the text will be International English. Similarly for German reformed, Swiss German, Swiss Reformed German, Spanish, French, Portuguese etc.
To change the language on the text you can either modify the character style sheet to have that language which you want your text to be spell checked in or go to the measurement palette character tab and change the language from the drop down available. Once you verify that the text language is the one you intended to be then run the spell check utilities like the AutoCorrectXT Spell Check Story option from the Utilities menu AutoCorrectXT option. While marking the misspelled words as red underlines the dictionary used for spell checking will be picked based on the text language.
Once the text is spell checked in the respective language the hovering menu will give suggestions in the same language and then you can select the correct suggestion from the menu. Spell checking is made so easy by AutoCorrectXT in QuarkXPress that even a naive publisher can use it to be effective and efficient.