Voz danas ide sporije nego juče.

Serbian does not have articles like a and the. So voz can mean a train or the train, depending on context.

In this sentence, English would usually say the train, but Serbian simply says voz.

Ide is the 3rd person singular present form of ići, meaning to go.

With vehicles, ići often means things like:

• to go
• to move
• to run
• to travel

So Voz danas ide sporije means something like The train is going / moving / running more slowly today.

It can correspond to either goes or is going, depending on context. Serbian present tense often covers both the English simple present and present progressive.

So this sentence could describe:

• what the train is doing right now, or
• how today’s train service is operating today in general

The exact English translation depends on the situation.

Because sporije is an adverb, while sporiji is an adjective.

Here, the word is describing how the train goes, so Serbian uses an adverb:

• spor = slow
• sporo = slowly
• sporije = more slowly / slower

Compare:

• sporiji voz = a slower train
• ide sporije = goes more slowly

The pattern here is:

comparative adverb + nego + comparison point

So:

• sporije = more slowly
• nego = than
• juče = yesterday

That gives sporije nego juče = more slowly than yesterday.

Nego is the usual word for than in comparisons like this.

In this sentence, the comparison is between today and yesterday, so nego is the natural choice:

• danas ... nego juče = today ... than yesterday

It links the comparative idea very much like English than.

Because Serbian often leaves out repeated words when they are easy to understand from context.

English often says:

• The train is going slower today than it did yesterday

Serbian can express the same idea more briefly:

• Voz danas ide sporije nego juče

The idea than it went yesterday is understood, so the extra verb does not have to be stated.

Here, danas and juče are adverbs of time:

• danas = today
• juče = yesterday

So they are not functioning as nouns with case endings in this sentence. They simply tell you when something happens.

Yes, Serbian word order is fairly flexible. Voz danas ide sporije nego juče is a neutral, natural order, but other orders are possible for emphasis.

For example:

• Danas voz ide sporije nego juče puts more focus on today
• Voz ide sporije danas nego juče is also understandable, though less neutral

The basic meaning stays the same, but the emphasis shifts.

Both can appear in comparisons, but they are used in different kinds of structures.

A useful rule of thumb is:

• nego is common when comparing with a clause, adverb, or situation-like expression
• od is common when comparing with a noun or pronoun

Examples:

• Voz danas ide sporije nego juče = The train is going slower today than yesterday
• Voz je sporiji od autobusa = The train is slower than the bus

So in your sentence, nego fits because juče is a time expression, not a noun being compared directly as an object.

Not directly. Ide sporije means goes more slowly or is moving more slowly.

If you want to say the train is late, Serbian would more directly use kasni:

• Voz kasni = The train is late

Of course, if a train is going more slowly, it may end up being late, but that is only an implication, not the literal meaning of this sentence.