Not that I have any say in the matter, but…
Overall this looks good. You obviously did very thorough research. I, personally, would love to play as Liberia. But here are some minor suggestions:
Denmark already has a gunboat, most likely a reference to their Gunboat War against the British during the Napoleonic Wars. It's generally best to avoid overlapping unit names, especially with unique units. Unless you have a very specific reason for choosing the word gunboat to describe this unique Liberian ship, I would suggest renaming to something similar like, for example, "cutter."
Similarly, the Askari. It is a standard Capital Age (?) unit for the African culture civs. Making it also an Imperial Age "unique" unit for one faction of an Anglo culture civ is weird to me. Especially since I associate Askari more with the ruling colonial power (in this case, the Americo-Liberians) than the natives.
A more major issue than just names: I like the idea of invisible weapons but some of the seem a little powerful. Especially Kanga Oath, which is basically which is one of the Serbians' unique abilities. It is rather degrading to the Serbians that one of their only two unique abilities (the other being pretty situational) is stolen by another civilization for use among multiple other abilities. Like the names, try to keep it unique. As for the others, maybe if they all had a minor downside? Such as it also slower movement, or making the unit take damage, like Trample?
And finally, as much as I hate to say it, is Liberia really militarily significant enough for the mod and its time period? It seems they didn't really develop militarily until the 20th century and the world wars, for the most part beyond the scope of this mod. Let me restate, though: these are great ideas, and it would be awesome to play as Liberia.
Don't worry - any suggestion or idea is welcome, the devs just have to say: should I continue developing this or am I just wasting everyone's time.
Thanks for the naming ideas, BTW - never knew that "cutter" even existed
As I said before all of this is still in development - as I gather more and more books and whatall some names will change, as well as what they do or not.
As for invisible weapons - they should look powerful, because outside of cards, political upgrades and arsenal they do not have anything upping their HP and attack (hence Imperial only in name). In gameplay-terms this means that while some factions will stroll around with 1500 HP cannons and what not, Liberians in the Imperial Age will be lucky to have 300HP units. Invisible weapons are designed to counteract this.
Kanga Oath...hm...I have a idea as to how it should work but I have to confirm something...
And as for the significance, well, this is entirely subjective, but I'll try to explain my POV. Liberia and Ethiopia were the only two African nations that managed to maintain their independence during the turbulent Scramble for Africa - this alone is a pretty impressive feat, and while someone might say that if not for USA, the Brits and French would decimate them, I will say that if it weren't for Russians, Ethiopia would be an Italian-British colony to this very day.
Liberia is also the only actual, legit USA colony, created and supplied by many famous people, including Lincoln himself. Their story is a story of struggle, hardship and massive amounts of colorism from Americo-Liberians (who were mostly ex-slaves from Southern States or Caribs) towards Native Africans. Did you know that until the first civil war there the country was literally ruled by a Masonic Lodge? And yet no one talks about them besides the civil wars.
IMO they share the same fate as Paraguay or Mapuche, in that these nations have a very awesome history and cultures, that are (for the most part) completely unknown to all but the most hardcore history enthusiasts, due to limited amount of stuff available about them online or in English. Just like with them there are thousands of books about Liberia and the culture of their people, yet there is only like a solid 4% of them available online, if available at all outside of national libraries in USA. Not even Ebay and Amazon had what I wanted, which I consider to be a damn shame.
Concluding all of this, I believe that Liberia is a nation that deserves to be represented as a faction in the WoL mod not only because of their unique gameplay style and history, but also because of the fact how little people actually know about it. Having them as a playable faction will certainly gain at least some level of attention from both new and old players, just out of sheer "WTH is this shit?". This will only add to the popularity of the mod.
But than again - if the devs will greenlight it, I will continue to develop this, until they have a full design document on their hands. I can't code for shit, but that's the very least I can do. If not, then alas, just my bad luck, I suppose.