Safari seems to be modified I just ran this command and saw that Safari was modified.

$ codesign --verify -vv /Applications/Safari.app/
--validated:/Applications/Safari.app/Contents/MacOS/SafariForWebKitDevelopment
/Applications/Safari.app/: a sealed resource is missing or invalid
file modified: /Applications/Safari.app/Contents/Resources/English.lproj/InfoPlist.strings
file modified: /Applications/Safari.app/Contents/Resources/English.lproj/ServicesMenu.strings


My questions are:


Is there any way to see what exactly was changed? 
Why Safari could have been modified? (I didn't do it and I don't suspect a virus to change translations)


I'm running Safari 7.0.5 on OS X 10.9.4
The way to determine what changed is to diff the current folder against a backup copy from when the code sign was valid.

Why could be as simple and harmless as bit rot or a filesystem error and it could be that some other tool injected code.

Unless you routinely list and checksum each file in /Applications/Safari.app and compare those results, your best bet might be to re-install the latest combo updater from http://apple.com/downloads and re-check that the binary is properly signed. If not, you might need to back up that machine and start with a clean erase and reinstall and watch to see what / when Safari gets modified going forward.