Aseară am trimis un mesaj vocal.

Yes, aseară is one word, and it means last night / yesterday evening depending on context.

In everyday Romanian, aseară is a very common time expression. It refers to the evening or night of the previous day.

You can also hear ieri seară, which means basically the same thing.
So:

• aseară = last night
• ieri seară = yesterday evening / last night

Both are natural.

Am trimis is the compound past in Romanian, called perfectul compus. It is one of the main ways to talk about completed actions in the past.

It is built like this:

• am = auxiliary verb (have form for I)
• trimis = past participle of a trimite (to send)

So:

• am trimis = I sent / I have sent

Romanian often uses this structure where English might simply use the simple past.

The base verb is a trimite, which means to send.

In this sentence:

• a trimite = infinitive
• trimis = past participle
• am trimis = I sent

So the sentence uses the verb in a completed past action form.

Because Romanian usually does not need the subject pronoun if the verb already shows who the subject is.

Here:

• am trimis clearly means I sent

So eu is unnecessary unless you want emphasis or contrast.

Compare:

• Aseară am trimis un mesaj vocal. = Last night I sent a voice message.
• Aseară eu am trimis un mesaj vocal. = Last night I sent a voice message.
  This sounds more emphatic, as if contrasting with someone else.

In Romanian, adjectives usually come after the noun.

So:

• mesaj vocal = voice message
• literally: message vocal

This is normal Romanian word order:

• o casă mare = a big house
• un film bun = a good film
• un mesaj vocal = a voice message

English often puts adjectives before the noun, but Romanian usually puts them after.

Un mesaj means a message, so it is indefinite.

• un mesaj vocal = a voice message
• mesajul vocal = the voice message

Romanian marks definiteness differently from English. Instead of a separate word like the, Romanian usually adds the definite article to the end of the noun:

• mesaj = message
• mesajul = the message

So in your sentence, un mesaj vocal is correct because it means a voice message, not the voice message.

Mesaj is a neuter noun in Romanian.

Romanian neuter nouns behave:

• like masculine in the singular
• like feminine in the plural

So:

• singular: un mesaj
• plural: două mesaje

In this sentence, the adjective matches the singular form:

• un mesaj vocal

If plural, it would be:

• două mesaje vocale

Not exactly. In this phrase, vocal means something like spoken / by voice / audio.

So:

• mesaj vocal = voice message

Even though English has the adjective vocal, in this context English normally says voice message, not vocal message.

So this is a good example where a Romanian word resembles an English word, but the most natural translation uses a different form in English.

Yes, Romanian word order is fairly flexible.

The most neutral version here is:

• Aseară am trimis un mesaj vocal.

But you could also say:

• Am trimis un mesaj vocal aseară.
• Un mesaj vocal am trimis aseară.
  This one gives stronger focus to un mesaj vocal.

All of these are grammatical, but the first one sounds very natural because time expressions are often placed at the beginning.

Sometimes yes, but it is also just a very normal placement.

Putting aseară first helps set the time frame right away:

• Aseară am trimis un mesaj vocal. = Last night, I sent a voice message.

Romanian often puts adverbs of time near the beginning of the sentence, especially in everyday speech.

So it does not necessarily sound strongly emphatic; it can simply be natural organization of information.

A simple pronunciation guide is:

Aseară am trimis un mesaj vocal
ah-SYA-rə am tree-MEES oon meh-ZHAZH vo-KAL

A few useful notes:

• ă is a short central vowel, like the final sound in sofa
• j in mesaj sounds like the s in measure
• c in vocal is a hard k sound

Approximate word stress:

• aseară → stress on sea
• trimis → stress on the last syllable
• mesaj → stress on the last syllable
• vocal → stress on the second syllable

Yes, absolutely.

• Aseară am trimis un mesaj vocal.
• Ieri seară am trimis un mesaj vocal.

Both are natural and mean essentially the same thing.

Very roughly:

• aseară is shorter and very common in speech
• ieri seară is a bit more explicit and transparent for learners

You put nu before the verb:

• Aseară nu am trimis un mesaj vocal.

That means:

• Last night I didn’t send a voice message.

In speech, you may also hear the auxiliary and negative closely linked in rhythm, but the standard written form is:

• nu am trimis

A simple way is just to keep the same word order and use question intonation:

• Aseară am trimis un mesaj vocal?

But more naturally, if you are asking someone, you would usually change the verb person:

• Aseară ai trimis un mesaj vocal? = Did you send a voice message last night?

Romanian often forms yes/no questions through intonation rather than a special helper verb like English did.

It is neutral and natural in both spoken and written Romanian.

Nothing in it is especially formal or especially slangy:

• aseară = everyday
• am trimis = standard past tense
• mesaj vocal = standard modern vocabulary

So it is a very useful model sentence for normal conversation.