Even if you play offline modes like Career Mode, your profile usually accumulates Football Club Credits (FCC) and XP while connected to EA servers. These are the "currency" used to unlock items. Navigate to the Catalog : From the FIFA 14 main menu, select Football Club Filter by Gameplay : Use the tabs at the top to select the Purchase Kits
Since you are playing the full offline version of FIFA 14 PC, you do not need an internet connection to perform this unlock, but you do need a few tools: how+to+unlock+classic+kits+in+fifa+14+pc+offline+full
You now know . Go relive the glory days. Put on that 1990 Germany kit. Beat your friends offline with a throwback Maradona. Even if you play offline modes like Career
The most reliable way to get all kits (and often updated rosters) is through the FIFA Infinity Patch (FIP) . Go relive the glory days
For a visual walkthrough of the catalogue and how to navigate the Gameplay tab: How To Unlock Classic Kits In FIFA 14 YouTube• 16-Apr-2014 Critical Note for "Offline Full" Users If you are playing a version of the game where the EA Servers are disconnected