Just a note, not all -1's are added content. Before 1.7 we didn't use the dialog.tlk, so typo's and other grammatical errors got fixed as such. It's a lot easier to just modify the .tlk though, but remnants of the old method can still be found in a lot of .dlg files...
So you don't have to add new lines there into the .tlk, just find the proper entry, it should already exist (of course if you don't base it on english the -1's might not be there at all, don't know how they work).