Vreau să vorbesc cu ele diseară.

Romanian often drops the subject pronoun when it is clear from the verb ending.

• vreau already means I want
• vorbesc here also matches I speak / I may speak

So Vreau să vorbesc cu ele diseară is perfectly natural without eu.

If you add eu — Eu vreau să vorbesc cu ele diseară — it usually adds emphasis, like I want to speak to them.

This is a very common Romanian structure:

• vreau = I want
• să vorbesc = to speak

So the sentence is built like:

• Vreau = I want
• să vorbesc = to speak
• cu ele = with/to them
• diseară = tonight / this evening

Romanian usually uses a vrea + să + verb where English uses want + to + verb.

Because after a vrea (to want), Romanian normally uses să + a finite verb, not the infinitive.

So:

• Vreau să vorbesc = I want to speak

This is one of the most important differences from English.
English says to speak; Romanian usually says something more like that I speak in form, even though the meaning is simply to speak.

It is the present subjunctive, triggered by să.

After să, Romanian uses the subjunctive form. In this case:

• să vorbesc = that I speak / for me to speak
• in natural English: to speak

A useful thing to know is that for some persons, the subjunctive form looks exactly like the present indicative. So even though vorbesc looks familiar, after să it is functioning as a subjunctive form.

Because after a preposition like cu (with), Romanian uses a stressed pronoun.

So:

• cu ele = with them / to them
• not cu le
• not cu lor

Here are the stressed pronouns commonly used after prepositions:

• mine = me
• tine = you
• el / ea = him / her
• noi = us
• voi = you all
• ei / ele = them

By contrast:

• le is an unstressed clitic pronoun
• lor is often used for to them / their, but not here after cu

So cu ele is the correct form.

Because Romanian usually says a vorbi cu cineva — literally to speak/talk with someone.

So:

• vorbesc cu ele can mean I’m speaking with them
• and in many contexts also I’m speaking to them

This is very normal Romanian usage. English often prefers to in this kind of sentence, but Romanian commonly uses cu.

Yes, ele is the feminine plural form of they/them.

It can refer to:

• a group of women or girls
• feminine plural nouns
• sometimes animals or things, if the noun is grammatically feminine plural

If the group is masculine or mixed gender, Romanian normally uses ei instead.

So:

• cu ele = with/to them (feminine)
• cu ei = with/to them (masculine or mixed)

Diseară means this evening or tonight.

It is an adverb of time, and in this sentence it tells you when the speaker wants to talk to them.

So:

• Vreau să vorbesc cu ele diseară = I want to speak to them tonight / this evening

You may also see similar expressions such as:

• astă seară = this evening
• în seara asta = this evening / tonight

But diseară is a very common and natural single-word option.

Yes. Romanian word order is fairly flexible, especially with time expressions like diseară.

All of these can be natural, depending on emphasis:

• Vreau să vorbesc cu ele diseară.
• Vreau să vorbesc diseară cu ele.
• Diseară vreau să vorbesc cu ele.

The basic meaning stays the same, but the emphasis shifts a little:

• putting diseară first emphasizes when
• keeping it at the end sounds very neutral and natural

No. The infinitive is a vorbi = to speak.

Here is the difference:

• a vorbi = infinitive
• vorbesc = I speak
• să vorbesc = that I speak / for me to speak, usually translated as to speak after verbs like vreau

So in this sentence, vorbesc is not the dictionary form; it is a conjugated form used after să.