This is the Objective-C code:
NSString *text = NSLocalizedString(@\"Test \\\"this is a sample text\\\"\", @\"Test \\\"this is a sample text\\\"\");
Seems to be a bug in the way Xcode handles the .strings -> .xliff conversions, and so on. You'll have to wait for Apple to fix it.
.strings
.xliff
May I suggest using curly quotes in the meantime?
@"Text “this is a sample text”"
It seems to export to XLIFF properly.
It seems Xcode 6.3 fixed this bug.