Niciun coleg nu vine azi la birou, pentru că este weekend.

Niciun coleg means no colleague / not a single colleague.

Romanian normally uses a singular noun after niciun / nicio:

• niciun coleg = no male colleague / no colleague
• nicio colegă = no female colleague

So even though English often uses a plural idea like no colleagues, Romanian packages it as not even one colleague, which is why the noun is singular.

In modern standard Romanian, niciun and nicio are normally written as one word when they mean no / not a single / none.

So:

• niciun coleg = no colleague
• nicio problemă = no problem

You may still see nici un in older texts or nonstandard writing, but niciun is the recommended standard spelling here.

Because Romanian uses negative concord. That means if you have a negative word like niciun, the verb is also marked as negative with nu.

So standard Romanian is:

• Niciun coleg nu vine.

Not:

• Niciun coleg vine.

This is very normal in Romanian, even though English usually does not do this.

Because the grammatical subject is niciun coleg, which is singular.

So the verb agrees with coleg, not with the English idea of colleagues:

• niciun coleg vine would still need nu, so:
• niciun coleg nu vine

Compare:

• Un coleg vine = one colleague comes
• Niciun coleg nu vine = no colleague comes
• Colegii nu vin = the colleagues are not coming

Yes, vine la birou literally means comes to the office.

But Romanian and English do not always choose come/go in exactly the same way. In context, a veni la birou often just means to come in to the office / to show up at the office / to go to work, depending on perspective.

A Romanian speaker could also say:

• merge la birou = goes to the office

In this sentence, vine la birou is completely natural.

They both mean today.

• azi = shorter, very common, slightly more conversational
• astăzi = a bit fuller, sometimes a little more formal or careful

So:

• Niciun coleg nu vine azi la birou
• Niciun coleg nu vine astăzi la birou

Both are correct.

Because la birou usually means to the office / at the office / at work in the sense of the workplace.

• la birou = at the office, to the office, at work
• în birou = in the office room, inside the office

So here:

• nu vine azi la birou = is not coming to the office today

If you said în birou, it would sound more like physical location inside a room.

Pentru că means because.

It is a very common and neutral way to give a reason:

• ..., pentru că este weekend. = ..., because it is the weekend.

Other possible conjunctions are:

• fiindcă = because
• deoarece = because / since, often a bit more formal

Also notice the spelling:

• că with ă, not ca

That accent matters, because că and ca are different words.

Because Romanian does not need a dummy subject like English it in sentences such as it is late, it is raining, or it is weekend.

So Romanian simply says:

• este weekend = it is the weekend
• este târziu = it is late
• plouă = it is raining

This is very normal. Romanian often leaves the subject unspoken when it is obvious or when English would use a dummy it.

Yes, weekend is a very common loanword in Romanian.

And in expressions with este / e, Romanian often uses a noun without the definite article when stating a general situation or label:

• Este weekend. = It’s the weekend.
• Este vacanță. = It’s vacation / holiday time.

You can also hear:

• E weekend. = It’s the weekend.

If you use weekendul, that usually sounds more specifically like the weekend as a particular one in context.

Yes. In standard Romanian writing, a clause introduced by pentru că is very commonly separated with a comma when it comes after the main clause.

So this is natural:

• Niciun coleg nu vine azi la birou, pentru că este weekend.

In very casual writing, people may be less careful with commas, but the version with the comma is the safe standard choice here.

Yes. Romanian word order is fairly flexible, and moving parts of the sentence often changes the focus rather than the core meaning.

For example:

• Niciun coleg nu vine azi la birou. = neutral
• Azi, niciun coleg nu vine la birou. = emphasizes today
• La birou nu vine azi niciun coleg. = more marked, stronger focus on the office or the whole negative statement

The original sentence is a very natural neutral order.