Ju pli mi lernas Esperanton, des pli simpla la gramatiko fariĝas.

It is the standard way to express a correlation like the more ..., the more ... or the more ..., the less ....

So:

• Ju pli mi lernas Esperanton = The more I learn Esperanto
• des pli simpla la gramatiko fariĝas = the simpler the grammar becomes

A few similar examples:

• Ju pli mi praktikas, des pli bone mi parolas.
  The more I practice, the better I speak.
• Ju malpli mi dormas, des pli laca mi estas.
  The less I sleep, the more tired I am.

So ju introduces the first side of the comparison, and des introduces the matching result.

Pli means more.

In this sentence, it appears twice:

• Ju pli mi lernas ... = the more I learn ...
• des pli simpla ... = the more simple / the simpler ...

Esperanto often uses pli + adjective/adverb/verb idea instead of changing the word itself the way English sometimes does.

For example:

• pli simpla = simpler
• pli bona = better in a literal comparative structure, though pli bona is also the normal Esperanto form

So pli simpla is the regular Esperanto way to say simpler.

Because it is the direct object of lernas.

In Esperanto, the direct object usually takes the accusative ending -n.

• mi lernas Esperanton = I learn Esperanto
• mi legas libron = I read a book
• mi vidas la domon = I see the house

So here:

• mi = subject
• lernas = verb
• Esperanton = direct object

That is why Esperanto becomes Esperanton.

Because simpla is an adjective describing la gramatiko.

• simpla = simple
• simple = simply / in a simple way

Here, the sentence is saying that the grammar is becoming simple/simpler, so you need the adjective:

• la gramatiko estas simpla = the grammar is simple

If you used simple, it would be an adverb, which would not fit this role.

Because simpla is not a direct object here.

It is a predicate adjective linked to la gramatiko through the idea of becoming:

• la gramatiko fariĝas simpla = the grammar becomes simple

The subject is la gramatiko, and simpla describes that subject. Predicate adjectives agree with the subject in number and case when needed, but here the subject is singular and not accusative, so simpla stays just simpla.

Compare:

• La libro estas interesa.
  The book is interesting.
• La libro fariĝas interesa.
  The book becomes interesting.

No accusative is needed for interesa there either.

Because fariĝas means becomes, while estas means is.

That difference matters here:

• la gramatiko estas simpla = the grammar is simple
• la gramatiko fariĝas simpla = the grammar becomes simple

The sentence is expressing a change in how the grammar appears to the learner: as the speaker learns more, the grammar becomes simpler to them.

So fariĝas is a very natural choice.

It comes from the verb fariĝi, which means to become.

Breakdown:

• far- = do, make
• -iĝ- = become, get into a state
• -as = present tense

So:

• fariĝi = to become
• fariĝas = becomes / is becoming

The suffix -iĝ- is very common in Esperanto for the idea of entering a state:

• ruĝiĝi = to become red
• grandiĝi = to become bigger
• boniĝi = to improve, become better

Esperanto word order is more flexible than English word order.

The sentence says:

Ju pli mi lernas Esperanton, des pli simpla la gramatiko fariĝas.

But you could also say:

Ju pli mi lernas Esperanton, des pli simpla fariĝas la gramatiko.

Both are natural. The second may feel a bit more balanced to some learners because the verb comes before the subject in the second clause.

Esperanto often allows word order changes for style, emphasis, and rhythm, as long as the grammar remains clear.

In this sentence, la gramatiko is still the subject, and simpla still describes it.

Yes, but it is not exactly the same.

• ... fariĝas = becomes simpler
• ... estas = is simpler

With fariĝas, the sentence emphasizes a process or change over time. As you learn more, the grammar seems to become simpler.

With estas, the sentence sounds more like a static statement about degree at each stage.

So both can work, but fariĝas is usually the better choice if you want the idea of gradual change.

Because it refers to the grammar of Esperanto, not just a grammar in general.

• gramatiko = grammar
• la gramatiko = the grammar

In this context, the speaker means the specific grammar of the language being learned, so the definite article is natural.

Esperanto uses la for the, and it does not change form.

Language names normally do not take la when used in a basic way.

So:

• Mi lernas Esperanton. = I am learning Esperanto.
• Ŝi parolas la anglan. can appear in some contexts, but with language names the article depends on structure and style.

For Esperanto, it is very normal simply to say Esperanton with no article.

The important ending here is really the accusative -n, because it is the object of lernas.

Yes. Esperanto forms comparatives regularly with pli.

So:

• simpla = simple
• pli simpla = simpler / more simple
• la plej simpla = the simplest

This is completely normal Esperanto. Unlike English, Esperanto does not usually switch between endings like -er and separate words like more. It uses the same comparative system very consistently.

In normal interpretation, it means it seems simpler to the speaker as they learn more.

The grammar of Esperanto is not literally changing. What changes is the learner’s understanding of it. Esperanto often leaves that kind of idea implicit if context makes it clear.

So the sentence is understood as something like:

• The more I learn Esperanto, the simpler the grammar becomes to me.

That unstated personal perspective is very natural here.

A comma between the two parts is very common and helpful:

• Ju pli mi lernas Esperanton, des pli simpla la gramatiko fariĝas.

It clearly separates the two linked clauses. In practice, most writers would include it.

So while punctuation can vary somewhat in Esperanto, using the comma here is standard and recommended.

Yes. It is a very productive pattern.

Examples:

• Ju pli, des pli = the more, the more
• Ju pli, des malpli = the more, the less
• Ju malpli, des pli = the less, the more
• Ju malpli, des malpli = the less, the less

Examples in full:

• Ju pli mi legas, des pli rapide mi komprenas.
  The more I read, the more quickly I understand.
• Ju pli mi laboras, des malpli da tempo mi havas.
  The more I work, the less time I have.
• Ju malpli vi zorgas, des pli trankvila vi estas.
  The less you worry, the calmer you are.

So once you know ju ... des ..., you can use it in many similar sentences.