Please realise that this guide is basically one big spoiler. The game is an hour long, go finish it, make your own attempts at decoding the language, then come here and argue with me about everything I got wrong. :)

Or in simpler terms: HERE BE SPOILERS. They will ruin the experience for you if you read them before playing. Got that? Good, let's move on to more fun things!

This is the one bit of decoding that almost everyone instantly understands. The numbers can be found inside the "School" or Education Hub, in the first door, and are presented both as a row (zero to 9) and with simple math examples.

The small vertical line appears to be a plus (+) sign, while the small horizontal line is clearly a minus (-). So the simple math on the wall can be translated as:


And here's a funny little detail that will probably not amuse you as much as it amused me: When you come back out into the entrance of the "School", you may notice that the door leading into the 4 rooms has a sign on top of it saying: 1....4.

As in "Classrooms 1 to 4 to your left people, please don't dally in the entryway!" ;)

Understanding these numbers at the school is necessary for your higher education, namely for you to solve the professor's puzzle. The professor will present you with a sequence of 3 numbers and expect you to guess the other 3. He gets upset and deletes your progress if you make a mistake, but all you need to do in order to make him happy is to tell him the next 3 numbers of the Fibonacci sequence.


The first 6 Fibonacci numbers are 1, 1, 2, 3, 5, 8. You don't really need to know Signor Fibonacci to figure the puzzle out (though any puzzle gamer really should), you could also realize that 1+1=2, 1+2=3, 2+3=5, 3+5=8.

Other than that, Mr Professor is too pleased with your progress to keep talking to you, so let's move on.

This world seems to be a very sentimental place because you can find graffitis with the signs for the basic emotions all over the walls.



Even better, the computer translator is more than happy to confirm our suspicions about their meaning. Namely:

Happy

Surprised

Angry

Sad

The locals apparently don't care much about your own feelings, so attempting to tell them you're happy doesn't seem to get you far. However, they will occasionally tell you how they feel about a subject when asked, and occasionally they seem to even try and express complex emotional states by using them together. More on that later. For now let's continue with more...

The machine translator of this world doesn't appear to be updated often, because it's definitely missing some of the world's words. It will return a big angry "X" when it doesn't know what you're talking about - which will be most of the time. For example, it doesn't appear to understand the numbers or how to say "hi". However, when it's helpful it's super helpful and gives decent visual cues for some important words, aside from the emotions we explained before. Let's take them one by one.

You can locate this curious double triangle sign on a building in the far right of the world.

Inputting it in the computer gives us an image of two tools.

They look like digging tools, and digging is hard work, so let's call this symbol "WORK". We don't really know if it means work as in "Job" or work as in "Are you busy right now?", so we may need to test this with the locals.

The "Education Hub" or school is full of the lopsided E sign.

You can even see it on the right of the computer-translator's monitor.

Inputting it gives us a nice picture of a little blob sitting on a chair in front of a desk/table.

Personally, I think we have enough clues to call this sign "EDUCATION", "School" or "Learning". This is likely one of the very first signs people will attempt to input to the computer, because of how many times it is repeated inside the "school" (and because it's right there for you to copy when you talk to the machine), so it looks likely that this was the developer's attempt to help us "learn the language". The fact that it resembles an E for Education doesn't hurt either. (Interestingly enough the sign also resembles the Russian letter "Ш" for "Школа" or the Yiddish letter "ש" for "שולע", both meaning school. Thanks to cit.rus for pointing this out in the comments!)

You are likely to first input this one after you try to talk to one of the locals. If they don't understand what you're saying, they'll probably just return this "Huh?" sign.
The machine confirms that it's a question mark.
Let's call this the "WHAT?" sign.

This one is more obscure. When inside the "bar", you keep seeing repetitions of this glass-like symbol.
There is even one under the turbine painting/schema on the wall. In theory, it would be a rather safe assumption to call this sign "alcohol" or "fuel" (which many consider synonyms.... ahem). However, neither the computer nor the inhabitants seem to respond to it. Maybe they live to be a thousand years old and consider your character too young for that? ;)

What does the trick is removing the middle horizontal line.
The speech bubble clearly means "talk", "conversation". I call this the "CHAT" sign, or otherwise the "How do you do?"

It's unclear whether that middle horizontal line is there intentionally, in which case these are two separate words, or whether something was just overlooked by mistake. Everyone who discovered the sign so far seems to have done so by trial and error or by accident, and no one has offered a good explanation about it.

This sign is vaguely represented at the pedestals of the "classrooms hallway", if you squint.
But even if you don't spot it there, anyone attempting to decipher this language will eventually come to the idea of connecting all the dots. Doing that at the computer returns an image of your character, male or female depending on your initial choice.
There's a few interesting questions about what this sign actually means, and I've read some clever theories about it, but I'll keep them for a later section. Let's call it "self" or "identity" for now.

Okay, so here's the fun part. We've read through the back pages of our Lonely Planet booklet, and armed with our 15 or so words, we feel fully confident that we can engage in meaningful conversations with the locals. What could possibly go wrong?

I'm going to be making tons of assumptions in this segment, that I have no way of confirming. In other words, I'm more or less making things up as I go. Please do feel free to disagree with me in the comments!

Clearly, the first thing we should do is greet the friendly folk, but sadly we don't seem to have learnt the word for that yet. Unless of course one was super observative when they first arrived in the world.
You can't reenter that room after finishing the game, so you may have missed it. The computer also has nothing to say on the matter. But the locals are much more helpful.
Not only do they say "Hi" back, you also get to wave at each other.

After the waving, it would be nice to ask them how they're doing. In which case most people seem to indicate that they're happy, or at least happy you asked them. In polite society this would be translated more or less as follows:
You: How do you do?
The Local: Good, thank you! *smile*.

Grandma breaks the mould, featuring a peculiarly surprised expression. Maybe people in her world don't talk to the elderly (shame on them), and she's pleasantly surprised. Maybe it's just a shock to her that an alien creature can speak her language. In that case, I imagine the conversation went something like this:
You: How do you do?
Grandma: Oh my goodness, it speaks our language! I'm surprised and mildly spooked! Please don't attack me!

If grandmas in that world are anything like ours, then this conversation sounds very plausible to me.

Now clearly, this sounds almost like an impertinent question, but in your defense you're asleep. Plus, you are curious about this new world, and want to hear about people's education in order to get to know them better. I hope you realize that understanding their answers in this case will likely be a bit dodgy, seeing how you currently have the vocabulary of a badly trained Chihuahua. So let's start easy.

It appears that the farmer has no complex opinion on the matter and his school years were spent unusually happily. Or maybe he's just nodding and smiling politely because education is simply not a subject he cares much about.
You: So what was school like for you here in pixel land?
Farmerboy: Yes, yes, fine, thanks for asking, it was good.

The barwoman seems willing to divulge more, but unfortunately you have no clue what she's saying because your dictionary doesn't include that word. But in good tourist tradition, let's assume all the words that exist are the ones we know, and try to figure this out: This sign could theoretically be made out of the signs for happy and surprised. In that case, maybe the barwoman is telling you that she was shocked and pleased that she managed to get her high school degree. (Yes, indeed, I'm horribly stereotyping, but so do you when you travel abroad, admit it.) Alternatively, this could mean more or less:
You: So tell me about your education!
Barwoman: I'm pleasantly surprised you'd ask me such a question, most people assume I'm an idiot. School was great!

Grandma also has an interesting answer to offer, but again, you fail to understand a word she says. Still, if these are the signs for "Nope, wrong" / "Angry" and "Sad", then conceivably the conversation could have gone along these lines:
You: Grandma, how was school for you back in the day, do you remember?
Grandma: Stop being impertinent, child! I refuse to answer such questions, thinking back to those years makes me feel old and sad!

Asking folks abroad about their work seems to be the done thing, but not everyone will react well to that. Let's keep flying with the unsafe assumption that the locals are sensitive people who talk a lot about their feelings and try to translate their answers.

Grandma is the easiest one to start with. Clearly she is unhappy to be retired, and/or very busy. Taking care of 17 cats while maintaning your hat in pristine condition can't be an easy task.
You: Wonna talk about your work, grandma?
Grandma: Sadly, I happen to be retired. And by the way, this is a very unfortunate, and dare I say impolite, question to ask someone my age - your generation makes me sad, no manners whatsoever.

The barwoman is a bit more ambivalent in her answer, but she also works in customer service, so she can't exactly be angry at you even if she wants to. I'm going to assume that her answer is made out of the signs for happy and sad, which could either mean that some bar dwellers are jerks and make her life miserable but she can't (or won't) dwell on it, or that the job is lousy but the pay is good - yes, I do realize how unlikely that is, but hey, maybe in that world people actually tip well. On second thought, that's probably the other way around.
You: So how's work?
Barwoman: I like it! The job is nice and I'm happy meeting new people, but staring into my empty wallet when I buy my pack of noodles for the week makes me sad.

The farmer clearly has some issues with his chosen occupation. Apparently even mentioning the term work makes him angry and sad. Maybe he should have been less happy and more diligent at school.
You: So how do you like spending all your work day with a bunch of cattle?
Farmer: How dare you make fun of my work! I may be unhappy that I have to clean the manure of these space cows all day long, but you have no right to judge!

**More in Part 2, because Steam doesn't like long sections.**

Now that we've covered the basics, there's this itch to go into deep existential subject matters. Because obviously discussing philosophy is something everyone should try with suspicious grandmothers the world over.

So what happens when we try to ask the locals a question about the "self"? They all return the question/answer back at you. I will not claim to be great at discussing existence and the universe, but one simple way to look at this would be:
You: Who are you? Who am I? Who are we?
Everyone: I am me. You are you. We are we.

Now before I go on diving deeper into this puddle sized mystery, I'm going to quote a few things from this Steam discussion, because I found them interesting, and would rather not claim them as my own thoughts. Maybe they'll give you some extra ideas to ponder over:

引用自 Randolph Cherrypepper：

There is the "identity" symbol. That's a math term: identity means you get back what you put out there. [...] When you say the identity symbol, people always respond with the identity symbol. If you ask the machine about the identity symbol, it shows your character (even more reason I call it the identity symbol).

引用自 krlw890：

The "identity" symbol is the one I find the most interesting. It consists of every drawable line on the text/symbol-box, and, more interestingly, is the symbol you get if you were to draw all four emoticons on the text/symbol-box. This kind of follows with the recurring theme that the NPCs use when they combine emotions (to make the "big square," etc.).

What I found particularly fascinating, is that this subject of identity is echoed in the codified achievements.

There are 3 achievements you get when finishing the 3 puzzle segments, that initially look like gibberish. They are in fact the simplest possible substitution cipher, whereby you "roll back" the alphabet, that is, you replace each letter with the previous one in the alphabet. It results in this:

Zpv bsf uif wjmmbhf You are the village
Zpv bsf uif dsfbuvsft You are the creatures
Zpv bsf fwfszuijoh ifsf You are everything here

Looking at them together with the weird question of the "self" or "identity" sign, they seem to tell us something about the game that it shouldn't have taken us this long to figure out. Namely, when the Locals are asked about their identity and return the question, maybe that's because they're us: the protagonist of the game, and therefore also the player. And all their language and feelings, everything they talk about, it's all contained within this one identity. Considering that our hero is experiencing all this in a dream, this does seem almost too obvious in retrospect.

So the discussion appears to be rather simple to translate after all:
You: Who are you?
The Locals / The Creatures / The Village: We are you.

But hey don't ask me to go even deeper into what THAT means, I'm as shallow as the next person. ;)

It appears so. I couldn't find any other meaningful "words" or combinations that work either with the computer or with the locals and (judging from my short research) the internet seems to also not have found any more. For some people this may be a bit of disappointment, especially if they followed the development of the game. You see, the developer talked a bit about the language he was trying to create in this devlog post, and he more or less indicated that we would be looking at some kind of a grammar/syntax that consists of adding single strokes to words in order to create sentences. To the best of my understanding, this doesn't seem to be the case in the finished game. For what it's worth, I honestly believe that for a short free game like this one, expecting to create a fully fledged language with its own special grammar may have been a bit of an overreach.

Oh and since we're on the subject of whether that's all: How long did you spend trying to open the 3rd and 4th classroom doors? Hopefully not too long, because they simply don't open yet. Here's the post where the developer [MISP]Ludipe explains why:

Those two doors lead to small puzzles which were designed by devs from other games(kind of a cameo). They aren't finished yet, we thought they would be ready for release, but we'll have to wait and update the game the game once they send me all the data.

(Give me a nudge if you're reading this guide after the doors have opened, and I'll try to update it if there's anything relevant in there.)

Thank you to everyone posting their thoughts and discoveries in the forums here as well as over at Jayisgames.com, reading your ideas helped shape up mine. I'm especially grateful to Randolph Cherrypepper, your rundown from the post I quote was lots of help. Also thanks to Jaeguins who made a similar guide here, it gave me the idea to try and see what I could do with the language if I collected all the screenshots together.

My special thanks and a cookie to the devs for an interesting little gem that kept me more fascinated than it had any right to.