I am a native Polish speaker, I read Lem's books in original, so I will try to describe what traces of meaning I see when I read this sentence.
First, let me do a grammatical analysis of this sentence. This is a present tense indicative sentence (so, "somebody does something" or "somebody is doing something"). The subject is "udłamatyk". It is a masculine singular noun - I recognize this form by "-atyk" suffix, which is definitely masculine singular (compare with "matematyk", which means "a mathematician"). The verb is "fita". It is a singular verb, indicative, present tense - I recognize this form by "-ita" suffix (compare with "wita", which means "greets"; or "zgrzyta", which means "it grinds", "it scrapes", "it rasps" or "it grates").
So this sentence says that somebody (or something) called "udłamatyk" does something which is called "fita".
Then "wywjechnięty" is an adjective which describes this "udłamatyk". Or, more precisely, it is a verb participle (you know, verb participles are words like "broken" - which behave like adjectives, but they derive from verbs). It is singular, masculine, perfective. I recognize this form by "-nięty" suffix (compare with "kopnięty", which means "kicked"). It is clearly derived from a verb "wywjechnąć" (which, of course, like almost all other words I talk about, do not exist in Polish).
Ok, so we have a subject ("wywjechnięty udłamatyk"), we have a verb ("fita"), but what is the object? It is either the word "prencyk" or the whole phrase "prencyk a^n trencyk" - I assume the latter. Both "prencyk" and "trencyk" are nouns, singular, masculine, diminutives. From their suffix ("-cyk") we seem that they are either in nominative or accusative case (because for such nouns both forms are the same) - but from the context we see that it is accusative (object of a phrase can't be in a nominative case).
And then we also have "w kosmatni" - where "w" means "in", and "kosmatni" is a noun in locative case, feminine, singular. Nominative case of this word would be "kosmatnia". So "w kosmatni" means "in a place called 'kosmatnia'".
Taking this together, the sentence mean:
Something called "udłamatyk", which is "wywjechnięty", is doing "fita" to something called "prencyk a^n trencyk" in a place called "kosmatnia".
Now we can try to find out what these words mean. Like, of course then mean nothing (except "w", which means "in"), but they have some sparks of meaning, they resemble and suggest some meanings.
Let's start with "udłamatyk". This noun has suffix "-yk". This is a singular masculine noun. So definitely it is one thing, but what thing? It is a masculine noun, so definitely to my Polish ear it has some masculinness, but it doesn't necessarily mean that it is a male person. It may be a thing, in which case the masculinness doesn't mean much. In Polish each noun has a gender - masculine, feminine or neutral - and nouns which are not persons have arbitrary gender assigned by linguistic tradition: for instance "widelec" ("a fork") is masculine and "łyżka" ("a spoon") is feminine. Which doesn't mean that we, Poles, seriously believe that spoons can get pregnant, or that forks have moustache, but on the other hand a fork has - at least for me - some aura of masculinity around it. Which may be hard to imagine for a person who speaks only English, but you can think about the way in which red is a warm color and blue is a cold color - you know you can't burn yourself with a red crayon, but it really has some aura of hotness. And, for instance, if you have a children's book in which forks and spoons are alive and talk with each other, then for sure forks will be males and spoons will be females.
Ok, so "udłamatyk" is somehow masculine. What else can we know about it? It has "-yk" suffix. This suffix (or very similar "-ik" suffix) is often used to create a noun which denotes a person who does something or lives somewhere. For instance, "Europejczyk" is "a European person". Notice that here Polish is more precise than English: in English "European" can be both a noun and an adjective, while in Polish "Europejczyk" is a noun, while adjective is "Europejski". Similarly "Andaluzyjczyk" is a person from Andalusia, "Chińczyk" is a person from China, "Brazylijczyk" is a person from Brasil... As I mentioned, suffix "-yk" (or "-ik") can also mean "a person who does something". So "matematyk" is "a mathematician" (a person who studies mathematics), "praktyk" is "a practitioner" (a person who practices something), "polityk" is "a politician" (a person who practices politics), "psotnik" is "a pranker" (because "psota" is "a prank").
But "-yk" (or "-ik") suffix can be also used to create diminutives. For instance, "a stone" is "kamień", so "a little stone" is "kamyk". And "a fire" is "ogień", so "a little fire" is "ognik".
And we also have some nouns which end with "-yk" but are neither diminutives nor names of people who do something. Like "patyk" - "a stick".
Ok, so say that we assume that "udłamatyk" is a male person. What else can we say about this person? It sounds similar to "matematyk" ("a mathematician"), so similar, that when I hear "udłamatyk", I immediately think about it being, maybe, something similar to a mathematician. But it also is very similar to a verb "udławić się", which means "to choke". More or less. Again, Polish is here more specific than English and there are several words which can be translated into English as "to choke" - "dusić", "dławić się", "udławić się", "zadławić się" (and some more). Words "dławić się", "udławić się", "zadławić się" mean "to suffocate because when you eat something, you could not swallow it and it blocked your respiratory tract". For instance, if somebody steals your food, you can curse him "a żebyś się udławił!" - which means "I wish that you choke on this food". Now, let's talk about the difference between "dławić się" on one hand, and "udławić się / zadławić się" on the other hand. The difference between them is perfectiveness. In Polish each verb is either perfective or imperfective. Imperfective verbs are used to talk about actions which are not finished (or for which the result is not that important), while perfective verbs are used to talk about finished actions. English speakers can think here about English pair of words "to search" / "to find". Both mean the same action, but they differ in perfectiveness. So now, when you understand this distinctness between perfective and imperfective verb, accept the fact that in Polish we have this distinction for almost all verbs. For instance, "to eat" can be translated as "jeść" (imperfective) or "zjeść" (perfective). And "udłamatyk" sounds like having something to do with "udławić się", which is a perfective verb meaning "to choke on one's food".
Much more simple is the situation of the verb, "fita". It is a singular verb, indicative, present tense. So it means "he o she or it does some action called <fitać>". It somehow resembles verb "wita" (which means "he / she / it greets") - other than that, no clue what could it mean.
Then we have a direct object of the sentence: "prencyk a^n trencyk". A strange phrase. Two singular masculine nouns ("prencyk" and "trencyk") connected with a mathematical formula "a^n". It doesn't give us any clue how this construction could work grammatically. What would it even mean to connect two nouns with "a^n"? No clue, it doesn't resemble anything. What makes it even more strange is that most of the words in this sentence don't sound mathematically. You know, language of math always has some serious aura surrounding it. For instance, if in English I say "knottarian topology of pseudo-local seeds" it doesn't mean much, but definitely it sounds like A Serious Math. If in Polish I say "topologia węzłowa ziaren pseudolokalnych" - same seriousity. But this sentence, these words? They don't sound seriously (for a polish ear). "Fitać", "prencyk", "udłamatyk" - they don't sound seriously, which stands in a contrast with this serious, mathematical notation "a^n". And these two nouns - "prencyk" and "trencyk" - sound very nonseriously. As you remember, suffix "-yk" can be used to form diminutives. In case of "udłamatyk" it sounds like this word can be, maybe, a diminutive. But in case of "prencyk" and "trencyk" they sound very much like diminutives (I don't know why this difference - this is what I feel when I hear them). And notice that these two words are very similar, they only differ with a first letter. It is something that is sometimes used in children poems and stories: like in a well-known children's rhyme about two neighbours called Paweł and Gaweł. Do these words give some more clue about possible meanings? Not much. "Prencyk" sounds a little like "piecyk" (a little oven), "trencyk" sounds like "trenczyk" (a little trench coat).
Now let's talk about shadows of meaning visible in an adjective (more precisely: a verb participle) "wywjechnięty". Which was created by taking unexisting verb "wywjechnąć" and combining it with a suffix "-ty". The relationship between Polish words "wywjechnięty" and "wywjechnąć" is like a relationship between English words "broken" and "to break".
The spelling of this word is strange: I don't know any word in Polish which would begin with "wywj-". Polish spelling is quite (much more than English) regular and following simple rules. If I hear a word, I generally know how to spell it, even if I hear it for the first time. But if somebody told me word "wywjechać" and I would have to write it down, I would spell it "wywiechać" (with "i" instead of "j"). This strange spelling gives this word a strange vibe.
"Wywjechać" starts with a prefix "wy-", which is often used to create perfective verbs, sometimes with a meaning which has something to do with an outside direction. For instance: "nosić" is an imperfective verb meaning "to carry", "wynosić" is a perfective verb meaning "to take something out". Another example: "jechać" is "to go (by car, train or another vehicle)" and "wyjechać" is "to leave (by car, train or another vehicle)". Sometimes the relationship between "X" and "wy-X" verbs does not follow this rule, or follows it only somehow, in a less obvious way: "śmiać się" is an imperfective verb meaning "to laugh" and "wyśmiać" is a perfective word meaning "to ridicule". Or: "grać" is is an imperfective verb meaning "to play", "wygrać" is a perfective verb meaning "to win".
So verb "wywjechać" seems to be perfective, describing an action which is finished, of which result we care, maybe having something to do with an outside direction.
This verb is similar to some real Polish words, which cast a semantic shadow on it. It is similar to "zwichąć" or "wywichnąć", which means "to have a luxation (joint dislocation)". It is similar to "wiecha" which means "a wisp (of hay or straw)". It is maybe a little similar to "wiocha" which is an augmentative form of "wieś" ("a village").
And finally let's take a look at "w kosmatni". It mean "in kosmatnia", where "kosmatnia" is not a real Polish noun, but it very clearly seems to be a combination of three real Polish words: "kosmos", "matnia" and "kosmaty". I mean, when we combine "kosmos" with "matnia" we get "kosmatnia" - which, as a side effect, begins with "kosmat-", which resembles adjective "kosmaty".
"Kosmos" is a singular masculine noun which is simple and easy to translate to English: it is "a cosmos".
"Matnia" is a singular feminine noun which literally mean "the bulging part of a fishing net that collects the catch", or some other type of hunting trap. But in everyday life nobody uses this word in a literal meaning - it is always used figuratively to describe a difficult situation from which you can't escape. So "on znalazł się w matni" ("he found himself in 'matnia'") means "he found himself in a mess, in a quagmire".
Here, Lem used a trick which he sometimes uses in his books: he combined two words which match each other, which snap like two fitting pieces of a jigsaw puzzle, looking at what meaning would emerge from the combination. It feels like "I Ching", or some other type of oracle. Other people throw sticks or stones or seashells and hope that the resulting shapes will reveal them the truth; Lem throws words and hopes that the results of their combination will reveal the truth. In this case "kosm-" (a root of words "kosmos" ("a cosmos"), "kosmiczny" ("cosmic") etc.) ends with a letter "-m", while "matnia" starts with a letter "m-" - so we can connect them (again, like two fitting pieces of a jigsaw puzzle). The fact that they fit each other so well (producing "kosmatnia") seems to reveal the fact that a cosmos, a universe is a trap, from which we can't escape.
And, by the way, noun "kosmatnia" is very clearly related to adjective "kosmaty" which means "shaggy", "hairy".
And this is why there are no good translations of Lem's books.
