The answer is, we do not know.

There are indeed some universal grammar features, Chomsky hypothesised that those are inborn to human brains. Even if that is true, alien brains can differ.

On the other hand, we have no idea of knowing if there could be a human language that differs markedly in some aspects from every known language, or indeed if there has been one. If the history went differently and the subsaharan languages died out, would we ever think that clicks can be incorporated into a language as normal phonemes? Without east Asian languages, would we consider normal to have a language without obligatory grammatical number or gender? Without Vietnamese, would it seem possible that language can function without personal pronouns? Without ergative languages, would it ever occur to us that the subject might not be in the nominative? Limiting the focus to Europe, without Polish and Russian, would we realize that the colour "blue" can be analyzed as two different colours? Likewise, with Hungarian, the same goes for "red". Whatever you consider normal in your language, some other language on the Earth breaks it.

For really alien concepts: consider sign languages. Not the medium of expression, but the grammar. It is still highly linear, but there are some parallelisms. And some sign languages can create pronouns "on the fly" (in other words, they have infinite number of them). Yet, these are normal, widely used human languages.

For constructed languages created by humans, but deliberately breaking some of those language universals (and thus being extremely hard to learn), see loglan/lojban for languages based on predicates, or the stack based language Fith.

The answer is, we do not know.

There are indeed some universal grammar features, Chomsky hypothesised that those are inborn to human brains. Even if that is true, alien brains can differ.

On the other hand, we have no idea of knowing if there could be a human language that differs markedly in some aspects from every known language, or indeed if there has been one. If the history went differently and the subsaharan languages died out, would we ever think that clicks can be incorporated into a language as normal phonemes? Without east Asian languages, would we consider normal to have a language without obligatory grammatical number or gender? Without Vietnamese, would it seem possible that language can function without personal pronouns? Without ergative languages, would it ever occur to us that the subject might not be in the nominative? Limiting the focus to Europe, without Polish and Russian, would we realize that the colour "blue" can be analyzed as two different colours? Likewise, with Hungarian, the same goes for "red". Without English, would we consider normal that every noun can be verbed? Whatever you consider normal in your language, some other language on the Earth breaks it.

For really alien concepts: consider sign languages. Not the medium of expression, but the grammar. It is still highly linear, but there are some parallelisms. And some sign languages can create pronouns "on the fly" (in other words, they have infinite number of them). Yet, these are normal, widely used human languages.

For constructed languages created by humans, but deliberately breaking some of those language universals (and thus being extremely hard to learn), see loglan/lojban for languages based on predicates, or the stack based language Fith.