EDIT: I made lots of bad assumptions in this post, as I later discovered, especially after reading this old apolyton thread, in which some of the things I decry as nonexistent and impossible below are (or once were) shown to be not only possible but extant indeed.
Short answer: No way.
Longer answer: Definitely not an entire scenario, but parts of some components (Map, Art) would be theoretically extractable via some (currently nonexistent) conversion program.
Long, Long answer:
Hans, this is a hurculean ask. There are no utilities currently that can do this. It's probably completely possible to convert a Civ2 Scenario into Freeciv with 90%+ fidelity, but it would be
entirely manual with (maybe) 2 partial and potential exceptions:
1. The (raw) Map
Raw (underlying terrain) maps should
theoretically be extractable by a program, since both engines use text with letters in an array to store underlying map terrain. You would already have to have the ruleset and art complete for freeciv to interpret the map correctly, of course, which brings us to...
2. The Art
Art is easy enough to convert manually- to harvest art from a Civ2 scenario requires only rudimentary GIMP or Paint.net skills. To do it automatically, however...
might sort of work in some cases (like units and cities.. maybe terrain) but not in many others (extras, effects, etc) which are bundled awkwardly vs. Freeciv or even hard-coded to the Civ2 engine. In the case of units, which are always located on a grid, freeciv can already read those files natively- you would simply have to convert the Civ2 image's pink & purple diamonds to transparency, then find and map the grid's XY dimensions onto a freeciv units.spec... but you'd still have to rebuild the spec file itself manually to map the units.
Nations, Events, Effects, Rulesets (e.g. the guts) would have to be 100% manual, or else would require thousands of hours of coding a converter. At least you could copy-paste any text!
After all that is done... THEN the save file itself/map positions data would probably be easy enough to import via program... but it still wouldn't be trivial.
This is a really rosy picture I'm painting, isn't it?
I get the question, though, since some open source projects are 'engine reimplementations only' that, from the outset, make
reading the retail game's asset files a design goal (or requirement) (OpenMW, OpenXCOM...)- but Freeciv isn't like that. It is a complete redesign (Engine
and asset structure) that arrives at a game that plays similarly to Civ2... but there's little commonality under the hood, except high-flying concepts like "use rulesets to define rules" and "use sprite sheets and spec files to define art".