Hello, it all depends what version you are running. for CC or CS6 via creative cloud, change the language of the CC application, then reinstall with that language. You will be then be able to change the language of Photoshop via preferences/interface. For older version, there is a way to remove a file, but it's not officially supported. (google can help)
I had the same question minutes ago, and got this answer (from polish to english, but the prosedure is the same) and it worked perfectly! (I own a PS CC 2014 btw, still works the same way!)
Simply navigate to this directory: C:\Program Files\Adobe\Adobe Photoshop CS5.1\Locales\sv_SE\Support Files
the sv_SE folder is named such because my version is Swedish. Just find the similar named folder that looks like it should correspond with your language.
In the support files directory there will be a file named tw10428.dat
Make sure that photoshop is closed, change the file extension to .bak instead of .dat, and then restart photoshop.
Your software will now be in English.