DISCLAIMER:
This review is entirely for my own sake. You are welcome to read it but it may or may not contain spoilers for the whole game.

I expected a language with many symbols, meanings, structures and possible dialogues. The game does have a lot of symbols but once out of the tutorial you realize many (if not most) of them don't have a meaning/definition/use within the game. I understand that it is intentional that you can never get to know all of the intrincacies of an old extinct language, yet it's still a bit disappointing.
I also understand the linearity of the questions you are allowed a response to, as writing an answer for all possible prompts with correct syntax would be an insurmountable task; yet I still would have a enjoyed having a couple of side conversations about tangential topics that might not matter to the main path/story of the game.
Where I really think this game fails is at is how direct it is with what all symbols mean and wich ones you should use on your next prompt. There's almost no work from the player unless you force yourself to not open the notebook. I think the game would benefit from having an everpresent hint as to what the next topic of discussion should be but have the option to translate what the terminal answered and/or what your next prompt should be only for when you are feeling stuck or lost.
The good ending attempts to do a part of this by not having notebook pages attached to it at all, but by doing that there is no hint towards which is the only sentence that will get a response despite the fact that there would be many ways to continue the conversation.
The moment that felt the greatest while playing was when I had a streak of 4 consecutive questions without having opened the journal all flowing naturally like a conversation (or as naturally as a conversation with a computer in a different language can be) and then finally opening the notebook and seeing those four pages stating and outlining all of the deductions and logical steps I had done and followed on my own.

Overall, this was a good game for how cheap it is and I'm it exists and that I played it, but would probably recommend a few other "language games" over this one.

as a language geek i have mixed sensations about the game.

i love that the core, the central mechanic, is to decipher the language. i love the set up and the minimalist interface. but the implementation of how you learn the vocabulary and the syntax was frustrating for me because, almost all the time, the game tells you what to say, making it more linear in a bad way.

i prefered a better implementation of learning, like not only having the computer, but previous notes about other similar languages and scripts, with external resources and not a "notebook" that tells you the solution almost all the time. in a game like that i expected two things: resources and a notebook to really work with and take notes.

i neither liked that the conlang used was purely based in english and some syntax things from chinese, i really missed something more interesting, a phonology and a more credible conscript that i could write better on a notebook. some determinatives, bustrophedon? i dont know, but something with a twist.

don't get me wrong, is a cool game and i appreciate that it exists, but i wished something more with this setup and core mechanic

Grant Kuning set himself an impossible task when creating Sethian. Text parser games are already notorious for their inability to handle the full range of sentences players throw their way. One that operates entirely in an unfamiliar alien language is doomed from the start to magnify the inherent obtuseness of the form.

So it is that Sethian teeters between intense hand-holding, telling the player more or less exactly what to enter; and absolute inscrutability, with no clear way forward while the AI rejects even the most reasonable and well-formed sentences. I got the bad ending just by fucking around to see if I could find any sentence the game would recognize, and the good ending only by looking up a walkthrough online.

But despite its inevitable failure, it's hard not to be a bit intoxicated by the sheer ambition of what Sethian attempts to be. Where other games may incorporate decoding a language as a sidequest or step in a puzzle chain, Sethian makes it the heart of the experience. At its best comes close to the excitement of playing Her Story for the first time, feeling your way through a world of possible queries, the only boundary being your own limited vocabulary. It presents a challenge to designers who come after: what can you grow from the seeds that Sethian planted?

this game concept is just amazing. i can count on one hand the amount of genuine conlang-related experiential games like this, and it's such a cool market that needs to be tapped into more! sethian sets out to do a specific thing and it does it really, really well. yeah, there's some limits with not being able to literally have a conversation and there's a little bit of having to ask specifically what the game wants you to ask as opposed to jumping in real-conversation-style, but I kiiiinda think that that's on you if you expected fluid ai conversation. we don't even have that in real languages!