Они выбрали нового лидера.

Выбрали is the past tense plural form of the verb выбрать (to choose, to select).

It also shows perfective aspect, which means the action is viewed as completed. So the sentence presents the choice as a finished event: they chose / have chosen the leader.

Compare:

• они выбрали = they chose / they have chosen
• они выбирали = they were choosing / they chose repeatedly / they spent time choosing

So in this sentence, the focus is on the completed result.

The infinitive is выбрать.

This verb forms an aspect pair with:

• выбрать = perfective
• выбирать = imperfective

That is a very common Russian pattern. You often learn verbs in pairs:

• делать / сделать
• читать / прочитать
• выбирать / выбрать

In this sentence, the speaker chose the perfective form because the action is complete.

In Russian past tense, the verb agrees with the subject in gender and number, not person.

Here are the past-tense forms of выбрать:

• выбрал = he chose
• выбрала = she chose
• выбрало = it chose
• выбрали = they chose

So выбрали tells you the subject is plural. That matches они (they).

Unlike English, Russian does not need a separate verb form for I chose / you chose / they chose in the past based on person. The past tense mainly changes for gender and number.

Because нового лидера is in the accusative case, not the nominative.

The verb выбрать takes a direct object: they chose whom? what?
Here, the direct object is new leader.

For a masculine animate singular noun in Russian, the accusative looks like the genitive:

• nominative: новый лидер
• accusative: нового лидера

So both the adjective and the noun change form.

Because лидер is a masculine animate noun, and in the accusative singular, masculine animate nouns usually take the same form as the genitive singular.

So:

• nominative: лидер
• genitive: лидера
• accusative (animate): лидера

Since a leader is a person, it is animate, so the accusative becomes лидера.

If the noun were inanimate, the accusative would usually look like the nominative instead.

The adjective must agree with the noun in gender, number, and case.

Since лидера is:

• masculine
• singular
• animate
• accusative

the adjective must match it:

• nominative: новый лидер
• accusative animate: нового лидера

So нового is simply the correct agreeing form of новый.

Russian has no articles like a or the, so the sentence itself does not explicitly mark that difference.

Depending on context, it could mean:

• They chose a new leader
• They chose the new leader

Usually, context tells you which one is meant.

In many situations, English translators choose a new leader unless there is a specific previously mentioned leader.

Yes. Russian word order is more flexible than English because case endings show the grammatical roles.

The neutral/basic order here is:

• Они выбрали нового лидера.

But you could also say:

• Нового лидера они выбрали.
• Выбрали они нового лидера.

These alternatives can shift the focus or emphasis, but the basic meaning stays the same.

English relies much more heavily on word order to show who did what, while Russian can use endings for that.

You can often omit они in Russian if the subject is clear from context.

So Выбрали нового лидера can mean They chose a new leader, if the listener already knows who they are.

However, они is often included when you want to:

• make the subject explicit
• add contrast
• avoid ambiguity
• sound clearer in isolation

In a stand-alone example sentence, keeping они is very natural.

A good stressed version is:

Они́ вы́брали но́вого ли́дера.

Approximate pronunciation:

• Они́ = a-NEE
• вы́брали = VY-bra-li
• но́вого = NO-va-va or careful speech NO-va-go
• ли́дера = LEE-de-ra

A useful note: in normal speech, the г in -ого often sounds like в, so нового is commonly pronounced roughly like новава, even though it is spelled with г.

Yes. Russian past tense does not map perfectly onto English tense choices.

Because выбрать is perfective, они выбрали нового лидера can often be translated as either:

• They chose a new leader
• They have chosen a new leader

The best English translation depends on context. Russian is not making the same grammatical distinction that English makes between simple past and present perfect.

Они is in the nominative case because it is the subject of the sentence.

So the structure is:

• Они = subject, nominative
• выбрали = verb
• нового лидера = direct object, accusative

That is a very useful pattern to recognize in Russian sentence building.

No, лидер is a borrowed word, ultimately from English leader.

It is very common in modern Russian and is used naturally in contexts like:

• politics
• organizations
• sports
• business

Even though it is a borrowing, it behaves like a normal Russian masculine noun:

• лидер
• лидера
• лидеру
• лидером, etc.