Davide,
Prior to using your new port, I had a working Frescobaldi that I installed many months ago using a very cryptic and painful process that required a lot of manual work to get poppler, frescobaldi, etc installed. But, it did work.
Tonight I tried to use your new port. The port compiles with no errors. The macport install process failed when attempting to activate your Frescobaldi+devel saying that previous files exist. I did a check by attempting to deactivate Frescobaldi, but macports said there was not an activated Frescobaldi port. So I systematically renamed each file/folder using the mv comment as the port activate process for your new Frescobaldi port kept throwing up the errors. Eventually your port successfully activated.
And, it runs. But any attempt to open a file results in a cascade of errors. First set seem related to code-folding. Then there are more and eventually Frescobaldi crashes.
Now quite sure how to fix this. If macports said that there was no previous port I don't know how it could remove/clean it to make way for your port. Nor do I know enough to use a terminal (which I do know how to use) to remove things manually. Easy enough to use 'mv path path.old' as the port install was tossing out errors. Not so much to ferret out all the possible things that may be hindering your new port.
Any suggestions welcome.