The "Detailed Group Stats" in-game should always show you the correct values (I have updated it recently in several iterations), so please let me know if it displays incorrectly for some unit/terrain combination.
This shows that Dwarf does not get bonus in volcanic terrain (in fact I have now updated the wiki to show correct, i.e. it now shows Volcanic terrain as Combat Terrain: None).
I have also added Mountain as a choice in the terrain dropdown in the "Detailed Group Stats" popup (you need to delete offline cache for this to display properly though, otherwise it will show as
undefined as we didn't have any translation for Mountain in the system
)
Also, as you might have noticed, it is since a while back possible to select Ruins as a terraintype in this dropdown, and it will then correctly show your units with their individual UL added as terrain-bonus.
Also adjusted the tooltip for +battle in hill to read "+ battle in hill and mountain terrain" to make it more clear it is also valid for mountains.
Hope this clarifies