Our company is having the same problem (see post https://www-secure.symantec.com/connect/forums/there-way-change-feed-language-setting-without-changing-device-language).
I have a feed created with English set as the Feed Language and I also have the "Is Feed Default" checked. However, we have a few users that have their Ipad language set to French. Those users are not able to see the feed at all. Just to verify the issue I tested out 2 Ipads - one in English and one in French. The one in English pulled in the feed fine, but the French one did not. I then changed the language on each device to the opposite (English to French and vice-versa). After that the device that was originally set to French pulled up the feed fine and the one that started out with the feed no longer had access to it.
Some sort of "general" feed or solution to this would be wonderful as we have associates with BYOD devices from numerous countries that need to access our content. Asking users to change the language on their devices wouldn't go over well and trying to create and keep feeds up to date in every language needed would be an uneeded nightmare.