Robert Bowling, the Director of Communications / Community Manager for the Infinity Ward, has confirmed that the Cod 4 Variety Map Pack is Region Locked. Which means the Region (Language) of the Variety Map Pack, must match the Region that your Call of Duty 4: Modern Warfare disc is.
For those who have downloaded the wrong version, Rob says they are currently talking with Sony to see what option they'll have for PSN customers who purchased the incorrect version.
To quote: Hey Everyone - Heads up for international users purchasing the Variety Map Pack for the PS3. The Variety Map Pack is Region Locked, which means that you MUST purchase the version of the map pack which is compatible with the version of the Call of Duty 4: Modern Warfare Game Disc that you have.
If you have the GERMAN version of the game, you MUST purchase the GERMAN version of the map pack.
If you have the UK version of the game, you MUST purchase the UK version of the map pack.
Just make sure that the Disc version and the Map Pack version matches up. If you have an UK version of the game, DO NOT purchase a German version of the map pack. It won't work. The same goes for any other mismatched version.
For those of you who may have already purchased the incorrect language for the game disc you have, we are currently talking with Sony regarding any options you may have.
If you have any questions or concerns, please let me know. Thanks!