自由主義者 isn't "libertarian", it's "liberal"/"liberalist". If Yua wanted "libertarian", he would've gone with 完全自由主義, 自由至上主義, or 自由意志主義 instead of 自由主義.
While that WAS the historical meaning of the word "liberal" (see classical liberalism), the word has become so corrupted in everyday use (like Orwellian newspeak, really) that it can mean anything from social liberalism (i.e. the state must strike a balance between personal liberties and social equality) to economic liberalism (i.e. lassiz-faire economy) to progressives (this is what most Japanese would mean when he says リベラル) to classical liberalism to "all left-wing politics", or even as a generic insult for "anyone who disagrees with my political views".
To an average American, "liberal" is highly associated with New-Deal type social liberalism, i.e. Nanny state knows best. This is, in some sense, anti-classical liberalism, as personal freedoms are in some sense sacrificed for the "greater good". SJWs represents one type of American liberalism taken to an extreme.
Hibiki really doesn't fit the label of a liberal in most of the above senses. Especially not the American one. She emphasizes personal freedoms, yes (she's more or less a hedonist), but she wouldn't give a fig for social equality whatsoever. Or the economy, really.
From here we can see the best word to describe her is, after all, "libertarian", where (personal) freedom is of utmost importance.
When you translate, you do not just translate the literal meaning of the word, but also the general sense or effect the text has on the readers in the original language. "Liberal" is just plain confusing, especially considering English speakers (ESL or otherwise) all over the world have many conflicting definitions of the word. "Liberalist" is arguably even more so (it strongly suggests party membership and not just political ideology). "Libertarian" is the correct word to use in this case.
I thought liberalist was used in reference to Hibiki's other form "Bep" and the USSR. Although I agree that this Hibiki doesn't display any democrat liberalism mindsets. I like to see this Hibiki as an anarchist of sorts, the strongest thrive and the weak perish, and hedonism is the guiding philosophy.
While that WAS the historical meaning of the word "liberal" (see classical liberalism), the word has become so corrupted in everyday use (like Orwellian newspeak, really) that it can mean anything from social liberalism (i.e. the state must strike a balance between personal liberties and social equality) to economic liberalism (i.e. lassiz-faire economy) to progressives (this is what most Japanese would mean when he says リベラル) to classical liberalism to "all left-wing politics", or even as a generic insult for "anyone who disagrees with my political views".
I could have given you the benefit of doubt over this point had Yua written Shigure's dialogue so that she was using an informal term like リベラル. 自由主義, however, is a formal term used by academics, and AFAIK Occam's razor dictates that we should assume that Yua meant exactly what the term formally means in the absence of clear indications that the speaker (namely, Shigure) is not using it correctly.
To an average American, "liberal" is highly associated with New-Deal type social liberalism, i.e. Nanny state knows best. This is, in some sense, anti-classical liberalism, as personal freedoms are in some sense sacrificed for the "greater good". SJWs represents one type of American liberalism taken to an extreme.
The story isn't set in America, and nobody is compelling any of us to make the dialogue/narration of Japanese comics strictly fit into an American context. Accuracy and faithfulness to the source should never be set aside in favor of pandering to the perceived preferences of the target audience without a good reason.
Hibiki really doesn't fit the label of a liberal in most of the above senses. Especially not the American one. She emphasizes personal freedoms, yes (she's more or less a hedonist), but she wouldn't give a fig for social equality whatsoever. Or the economy, really.
From here we can see the best word to describe her is, after all, "libertarian", where (personal) freedom is of utmost importance.
First, you're acting like "libertarianism" is a monolithic ideology, when in fact it's not. In fact, it's divided into left, right, and socialist "variations" that are argued to comprise distinct ideologies in and of themselves in spite of their similarities.
Second, libertarianism is actually an off-shoot / subset of liberalism.
Third, libertarians are more than just about holding personal autonomy as sarcosanct; other major cornerstones of their beliefs are the relationship between the individual and the political state (typically in the form of advocating for minimizing or even outright abolishing it), and economics (anywhere from laissez-faire capitalism to communism). As far as I can remember, Hibiki has not exhibited any indications that she cares about politics or economics in any way (then again, neither have affected her personal life so far), and especially does not exhibit any signs of having any specific beef with authority figures (she gets along just fine with her Admiral).
Fourth, from what I gathered, libertarians (or at least, some of them) "believe that goodness is voluntary, morality is personal, human nature cannot be legislated away, and only harm to others should be illegal." None of this is even close to an accurate depiction of Hibiki's personality; in fact, so far her outlook on "harm to others" seems to be pretty much "I don't care if others harm each other as along as it doesn't affect me, and if I need to harm someone physically or emotionally to get something I really want, then so be it, even if it's my own sister."
In other words, Hibiki appears to only exhibit one element that is typical of libertarian ideologies, and ignores all the other elements entirely. She's a liberalist in a broad sense of the word
When you translate, you do not just translate the literal meaning of the word, but also the general sense or effect the text has on the readers in the original language. "Liberal" is just plain confusing, especially considering English speakers (ESL or otherwise) all over the world have many conflicting definitions of the word. "Liberalist" is arguably even more so (it strongly suggests party membership and not just political ideology). "Libertarian" is the correct word to use in this case.
None of this changes the fact that the Japanese have very specific terms for "liberalism" and "libertarianism". Hell, how do you know that "liberalism" in a Japanese context does not infact accurately apply to Hibiki? One only needs to look at how the European and American definitions of "liberalism" differ ("liberalism" and "conservatism" in economics are flipped around between the two spheres) to realize that what is "liberal" to one group may be very different in another group. To wit, Europe seems pretty much dominated by the socialist strain of libertarianism, with no significant presence of the other strains (probably a legacy of the Red Scare in the US).
In the end: Unless there is an unambiguous indication that Shigure or any other character is indeed misusing the term "liberalism" when talking about Hibiki, I do not see any good reason for assuming that Yua meant something else. That said, you could take solace in the fact that libertarianism is in fact considered a subset of liberalism (American libertarianism in particular directly adopted at its onset the elements of individualism and laissez-faire economics that originally were hallmarks of classical liberalism), so calling Hibiki a "liberalist" does not preclude her having some traits that one usually associates with libertarians.
I would characterize this Hibiki as ultra-cynical, rather than on a political spectrum.
It simply gives off the feeling of being a death flag, even. Pretty much what I expect from our resident sick puppy when she goes all out.Might as well just ask for something more... practical—in the material sense—instead, if you're going to the trouble to make a wish....I-I wished for my time here with everyone to be a more happy and enjoyable one.Mine... well, it's pretty much the same as Satsuki's, I think....that's quite Shigure-ish of you too.Here.So, what did you two wish for?Lemme see.To remain alive with everyone else until the end of the war.S-Stop it already please, you twooooo!Bit rich coming from the stark-raving mad liberalist...That's so like you, Satsuki. It's as though you were an angel.