La tassista mi ha detto che il traffico in centro è peggiore del solito.

Yes — tassista is a noun of common gender. The ending stays the same, and the article tells you whether the person is male or female:

• il tassista = the male taxi driver
• la tassista = the female taxi driver

So in this sentence, la tassista tells you the speaker is talking about a female taxi driver.

Mi means to me.

So:

• mi ha detto = told me
• literally: has said to me

Italian often uses an indirect object pronoun here instead of repeating a full phrase like a me.

Compare:

• La tassista mi ha detto... = The taxi driver told me...
• La tassista ha detto a me... = also possible, but less natural unless you want emphasis

Ha detto is the passato prossimo of dire:

• infinitive: dire = to say / to tell
• ha detto = said / told

It is formed with:

• ha = has
• detto = said

In everyday spoken Italian, passato prossimo is very commonly used for a completed past event, so mi ha detto means she told me.

Here che means that and introduces the next clause:

• mi ha detto che... = she told me that...

In English, that is often omitted:

• She told me that traffic is worse than usual.
• She told me traffic is worse than usual.

In Italian, che is normally kept.

Italian uses definite articles more often than English does.

So where English might simply say traffic, Italian often says il traffico.

Here:

• il traffico = the traffic

Even though English does not always use the, Italian usually does with nouns like this.

In centro is a very common idiomatic expression meaning:

• downtown
• in the city center

So:

• il traffico in centro = traffic downtown / traffic in the city center

Nel centro is possible in other contexts, but it usually sounds more literal, like in the center of something, or it may refer to a specific center. For talking about being downtown, in centro is the normal expression.

Because the taxi driver told the speaker that this situation is true now (or is still being presented as true).

So:

• mi ha detto che il traffico in centro è peggiore del solito
• literally: she told me that traffic downtown is worse than usual

Italian often keeps the present tense in reported speech if the statement is still considered valid at the time of speaking.

If you used era, it would suggest that it was worse at that past moment, without necessarily saying it still is now.

Because è is the verb is.

The accent distinguishes it from e, which means and.

So:

• è = is
• e = and

This is a very important spelling difference in Italian.

Peggiore means worse.

It is the comparative form used for bad/worse, so:

• peggiore = worse

And del solito means than usual:

• del = di + il
• solito = usual / the usual

So:

• peggiore del solito = worse than usual

This is a very common Italian pattern:

• più ... del solito = more ... than usual
• peggiore del solito = worse than usual
• meglio del solito = better than usual

Yes. In this sentence, English most naturally uses tell:

• La tassista mi ha detto... = The taxi driver told me...

But the Italian verb is still dire, which broadly covers what English often divides into say and tell.

A helpful way to think about it is:

• dire qualcosa = say something
• dire qualcosa a qualcuno = tell someone something / say something to someone

So here, because there is a person receiving the information (mi = to me), told me is the best English translation.