Ju pli frue ni alvenas al tiu vendejo, des pli mallonga estas la vico.

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

In this sentence:

• Ju pli frue = the earlier
• des pli mallonga = the shorter

So the whole pattern means:

• Ju pli frue ni alvenas..., des pli mallonga estas la vico.
• The earlier we arrive..., the shorter the line is.

A helpful way to remember it:

• ju introduces the changing condition
• des introduces the matching result

Because frue is an adverb, while frua is an adjective.

Here, frue describes when we arrive, so it modifies the verb alvenas (arrive):

• ni alvenas frue = we arrive early

Since we are comparing how early we arrive, Esperanto uses:

• pli frue = earlier

If you used frua, it would describe a noun, such as:

• frua trajno = an early train
• frua horo = an early hour

So in this sentence, frue is correct because it refers to the action of arriving.

Because mallonga describes the noun vico (line/queue), so it must be an adjective.

• la vico estas mallonga = the line is short

In the sentence:

• des pli mallonga estas la vico

the word mallonga is saying what kind of line it is: a shorter one.

If you used mallonge, that would be an adverb, and adverbs do not describe nouns.

So:

• mallonga = short (adjective)
• mallonge = briefly / in a short way (adverb)

Because it is not a direct object here. It is a predicate adjective after estas.

In Esperanto, adjectives take -n only when they must match a noun that has -n. But here:

• la vico is the subject
• mallonga describes the subject after estas

So we get:

• la vico estas mallonga

not:

• la vicon estas mallongan

That would be wrong.

Both are possible. Esperanto allows fairly flexible word order, especially with estas.

So these mean the same thing:

• des pli mallonga estas la vico
• des pli mallonga la vico estas
• la vico estas des pli mallonga (less natural in this exact comparative structure, but understandable)

The version in your sentence puts the focus first on the comparison:

• des pli mallonga = the shorter

Then it identifies what is short:

• estas la vico = is the line

This order is natural and stylistically smooth in Esperanto.

Because alveni normally means to arrive at/to a place, and Esperanto commonly uses al for the destination.

So:

• alveni al la vendejo = to arrive at the shop

In your sentence:

• ni alvenas al tiu vendejo = we arrive at that shop

English often uses arrive at or sometimes just arrive, but Esperanto usually makes the destination explicit with al.

Tiu means that.

So:

• tiu vendejo = that shop/store

It points to a specific store, not just any store.

Compare:

• vendejo = a shop / store
• la vendejo = the shop / the store
• tiu vendejo = that shop / that store

A learner may wonder why it is not la tiu vendejo. In Esperanto, you normally do not combine la with tiu. Tiu already does the job of pointing out a specific thing.

Esperanto often uses the present tense for general truths, habitual situations, or cause-and-effect statements.

So:

• Ju pli frue ni alvenas..., des pli mallonga estas la vico.

means something like:

• The earlier we arrive..., the shorter the line is.

This is a general rule, not a statement about one single completed event.

If you wanted to talk about a specific past situation, you could use past tense:

• Ju pli frue ni alvenis..., des pli mallonga estis la vico.
• The earlier we arrived, the shorter the line was.

No. Des pli mallonga is already complete and correct.

Here is how it works:

• mallonga = short
• pli mallonga = shorter
• des pli mallonga = the shorter in this comparison structure

So pli is already there. You do not need another comparative marker.

The phrase breaks down like this:

• des = marks the second half of the correlation
• pli mallonga = shorter

Because mallonga is the normal, natural word for short.

Compare:

• longa = long
• mallonga = short
• malpli longa = less long

In many situations, malpli longa is grammatically possible, but it sounds more literal and less natural here. A queue or line is normally described as:

• longa vico = a long line
• mallonga vico = a short line

So mallonga is the best choice.

Vico can mean a line, row, or queue depending on context.

In this sentence, because it is about arriving at a shop and the line becoming shorter, vico most naturally means:

• queue
• line

So la vico here is the line of people waiting.

Vendejo is a place where things are sold, so it can mean shop or store.

It comes from:

• vendi = to sell
• -ejo = place for

So literally, vendejo is a place for selling.

Depending on context, English might translate it as:

• shop
• store
• storefront
• sometimes market stall in a looser context, though that depends

Here, shop/store is the clearest translation.

Normally, no. In standard Esperanto, you keep estas here.

So the normal sentence is:

• des pli mallonga estas la vico

not:

• des pli mallonga la vico

Esperanto usually requires the verb esti when making this kind of statement.

Poetry or very informal style might omit words sometimes, but for learners, it is best to keep estas.

Yes, that is a useful way to understand it, but it is not a word-for-word translation.

The structure expresses a relationship:

• if one side changes, the other changes too

So in natural English, this sentence could be explained as:

• If we arrive earlier at that store, the line is shorter.

But the Esperanto pattern is closer to:

• The earlier we arrive at that store, the shorter the line is.

So if can help you understand the logic, but ju ... des ... is specifically a comparative correlation, not just a basic conditional.

Yes. It is often used with pli and malpli, but not only with them.

Examples:

• Ju pli vi legas, des pli vi lernas.
  The more you read, the more you learn.

• Ju malpli oni dormas, des pli laca oni estas.
  The less one sleeps, the more tired one is.

• Ju pli rapide ni laboras, des pli frue ni finos.
  The faster we work, the earlier we will finish.

In your sentence, it uses:

• pli frue = earlier
• pli mallonga = shorter

So this is a very common and important pattern in Esperanto.