Windows or Mac?
Two things to try:
1. LR relies on the regional preferences set in the operating system, and there have been a few users who have reported that those preferences got changed mysteriously. Go to the OS X System Preferences > Language & Region. Make sure the settings there are correct. Then click Advanced in the lower-right corner. Make sure that General > Format Language is correct, and then verify that the settings on the Dates and Times tabs are correct.
2. If that doesn't help, try resetting LR's preferences: http://www.lightroomforums.net/showthread.php?25197-Resetting-the-lightroom-preferences-fi le-updatedResetting the lightroom preferences file - updated - Lightroom Forums.That often fixes things when LR's user interface goes wonky.
If neither of those work, please add your vote and details of your situation to this problem report in the official Adobe feedback forum: Lightroom 2015.4 Mac in Spanish shows dates in English format | Photoshop Family Customer Community.
None of the suggested things works. Everything stays in English....
2016-02-03 20:07 GMT+01:00 johnrellis <email@example.com>:
Map names in Lr 6.4 created by johnrellis
<https://forums.adobe.com/people/johnrellis> in Photoshop Lightroom - View
the full discussion <https://forums.adobe.com/message/8459913#8459913>
I saw your post in the feedback forum -- that will make it a little more likely Adobe might notice. I'd guess that if this were a widespread problem among non-English installations, we'd see a lot more reports by now, so there might be something very specific to your configurations that are triggering the problem.