I doubt you will find a reliable method for doing a word count, if at all.
The words can be on a layout, in calculations, dialog boxes, custom functions, script steps etc etc
Using a DDR Report you would not be able to determine what is 'user viewable' text or what is from a calculation or script step etc.
At least... that's how I see it anyway. I may be wrong.
You can translate 'FileMaker' specific messages by editing a few files (With caution)
As an example (on windows) if you go into the Filemaker Folder, followed by Extensions, then English
you will see a file named FMStrs.dls (make a copy of this) then rename it to FMStrs.fp7
You can then open it in Filemaker
Switch to the layout FMStrings and you will some of the dialog messages there.
Of course, you then need to rename it back to FMStrs.dls when your finished.
I have never edited this file myself, so dont take my word for it that it will work successfully.
Using a resource editor, you can also change some dialog text in the FMRSRC.dll file.
I do remember this being documented in the past, although very briefly, I think it was in one of the FMP Advanced Developer Guides
Both of these files contain some special characters, which is used as a place holder, for things such as incrementing record counts etc.
Edit : Here is a link which briefly describes the few files :