SDL Trados Studio contains dictionaries for a number of languages. You can also add additional custom dictionaries.
To add an existing custom dictionary:
Select Tools > Options from the menu bar. The Options dialog box is displayed.
Select Editor > Spelling from the navigation tree. The Spelling settings are displayed on the right.
Click Custom Dictionaries to display the Custom Dictionaries dialog box.
Click Add to display the Add Custom Dictionary dialog box.
Enter the name of an existing dictionary in the File name box and click Save.
When you add a dictionary, the dictionary is valid for All Languages. You can modify the dictionary, so that it applies to just one language. Click here for more information about modifying a dictionary.