I wouldn't take advice on text in the user interface of my application from a guy who writes "im" instead of "I'm".
Bollywood: If you have a reasonable grasp of a language but don't know what words you should use in a Macintosh application, go to "System Preferences" -> "International" and drag the language you want to the top of the list. Restart some Apple applications and check out what they are doing.
But "Check Selected" and "Uncheck Selected" is not something you can just translate. You'll need to describe the context. Does "Check Selected" mean "each item has a checkbox; check the checkbox for all selected items" like in iTunes? That would be "Auswahl aktivieren" / "Auswahl deaktivieren" in iTunes German, and "Check Selection" / "Uncheck Selection" in iTunes English. And don't worry that the spelling checker doesn't like "deaktivieren", it is still correct. But you really, really have to describe the context.
PS. The translation that the translation widget gives for "check selected" wouldn't give a German the slightest clue of your intention. And "uncheck" doesn't translate, which is just as well.