Merkrede mia amikino venos por kafo, se ŝia rendevuo en la centro finiĝos frue.

Yes. Merkrede means on Wednesday.

In Esperanto, names of days can be used as adverbs with -e to mean on that day:

• lunde = on Monday
• marde = on Tuesday
• merkrede = on Wednesday

A learner may also see merkredon. That is also possible, using the accusative of time. So both can mean on Wednesday:

• Merkrede mia amikino venos...
• Merkredon mia amikino venos...

The -e form often feels a bit more adverbial, while the -n form is a common time expression too.

Because -in- is the feminine suffix.

• amiko = friend
• amikino = female friend

So mia amikino means my female friend.

Traditionally, amiko is the basic form and amikino specifically marks a woman. In modern usage, some speakers use amiko more neutrally in some contexts, but amikino clearly tells you the friend is female.

Because possessive words in Esperanto behave like adjectives.

• mia = my
• ŝia = her

Like adjectives, they normally end in -a and go before the noun:

• mia amikino = my friend
• ŝia rendevuo = her appointment/date

If needed, they can also take plural or accusative endings just like adjectives:

• miaj amikinoj = my female friends
• ŝian rendevuon = her appointment/date

Because -os is the future tense ending.

• venas = comes / is coming
• venis = came
• venos = will come

So mia amikino venos means my friend will come.

Esperanto verb endings are very regular, so once you know them, they are easy to recognize:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / jussive
• -i = infinitive

Because por does not take the accusative.

After a preposition like por, the noun is normally not marked with -n:

• por kafo = for coffee
• por manĝo = for a meal
• por vi = for you

So venos por kafo means something like will come for coffee or will come over for coffee.

Also, Esperanto often leaves out an article where English might say a coffee or just coffee, depending on context.

Esperanto has no indefinite article.

English distinguishes:

• a coffee
• coffee

Esperanto simply uses the noun:

• kafo

So por kafo can mean:

• for coffee
• for a coffee
• for some coffee

The exact nuance comes from context.

Esperanto does have a definite article, la, but no equivalent of English a/an.

Because Esperanto usually uses tense according to the actual time of the action, not according to a special English-style rule.

In English, we often say:

• If her appointment ends early, she will come.

Even though the ending is in the future, English uses the present tense ends after if.

Esperanto is more straightforward:

• se ŝia rendevuo finiĝos frue = if her appointment will end early

Since the appointment is expected to end in the future, finiĝos is natural.

You may occasionally see present tense in some contexts when the speaker wants a more general or vivid sense, but the future here is completely normal and often preferred.

Because finiĝi means to end or to come to an end, while fini usually means to end something or to finish something.

Compare:

• Mi finos la libron. = I will finish the book.
• La kunsido finiĝos. = The meeting will end.

Here, the appointment is not ending something else; it is itself coming to an end. So:

• ŝia rendevuo finiĝos = her appointment will end

The -iĝ- part often gives the sense become / get / come to be / happen by itself.

Rendevuo can mean several related things depending on context:

• an appointment
• a date
• a planned meeting

So in this sentence it could mean:

• a date in the city center
• an appointment in the city center
• a meetup in the city center

The context decides which English translation sounds best.

Because la centro refers to a specific center, usually understood from context as the city center or downtown.

• en la centro = in the center / in the city center

Using la often makes it sound like a known, identifiable place. That is very natural here.

Without la, en centro would usually sound less idiomatic in this situation, unless the speaker meant something more abstract or special-contextual.

Because frue is an adverb, and it modifies the verb finiĝos.

• frua = early, as an adjective
• frue = early, as an adverb

Here the meaning is will end early, so we need the adverb:

• finiĝos frue

If you used frua, it would need to describe a noun:

• frua rendevuo = an early appointment

Yes, it is normal and recommended.

In Esperanto, subordinate clauses are very often separated by commas, especially with words like:

• se = if
• kiam = when
• ĉar = because
• kvankam = although

So this punctuation is standard:

• Merkrede mia amikino venos por kafo, se ŝia rendevuo en la centro finiĝos frue.

It helps show clearly where the main clause ends and the if-clause begins.

Yes. Esperanto word order is fairly flexible because grammar endings do a lot of the work.

For example, these are all possible with slightly different emphasis:

• Merkrede mia amikino venos por kafo...
• Mia amikino venos merkrede por kafo...
• Por kafo mia amikino venos merkrede...

The original sentence begins with Merkrede, which puts a little emphasis on the time: As for Wednesday...

So the chosen order is natural and may slightly foreground Wednesday.

Not necessarily by grammar alone, but in this sentence that is the most natural reading.

• ŝia = her

So ŝia rendevuo means her appointment/date.

Since the previous subject is mia amikino, readers will normally understand ŝia as referring to that same person unless context suggests someone else.

If needed, Esperanto can repeat the noun for clarity:

• se la rendevuo de mia amikino finiĝos frue = if my female friend’s appointment ends early

That is less compact, but clearer if there might be confusion.