wǒmen shì yí gè duì.

Because 一 changes tone depending on the word that follows it.

Its basic pronunciation is yī (first tone), but in normal speech:

• before a fourth-tone syllable, it becomes yí (second tone)
• before a first, second, or third-tone syllable, it usually becomes yì (fourth tone)

Here, the next word is 个 gè, which is historically a fourth-tone word, so we say yí gè.

Even though 个 is often pronounced with a light/neutral tone in everyday speech, learners usually still learn this phrase as yí ge or yí gè.

个 is a measure word (also called a classifier).

In Chinese, when a number comes before a noun, you usually need a measure word in between:

• 一 个 人 = one person
• 一 个 问题 = one question
• 一 个 队 = one team

So 一 个 队 is the normal beginner pattern for one team.

English does not usually need this extra word, but Chinese usually does.

Usually, no.

队 is a noun, and if you want to say we are a team, Chinese normally uses a full noun phrase such as:

• 我们是一个队。

Without 一个, 我们是队 sounds incomplete or unnatural in standard Mandarin.

That said, in some special contexts, Chinese can drop words for style or slogans, but for normal grammar, 一个 is the safe and correct choice here.

Yes, literally it is one + measure word + team.

In Chinese, one + measure word + noun often corresponds to English a/an + noun.

So:

• 一个队 can mean one team
• in context, it can also simply mean a team

In this sentence, 我们是一个队 usually means we are a team, often with a slight sense of we belong together / we are one unit.

是 is the verb to be when linking the subject to a noun phrase.

Here:

• 我们 = we
• 是 = are
• 一个队 = a team

So the structure is:

Subject + 是 + noun phrase

This is similar to English We are a team.

In normal standard Mandarin, no.

When the predicate is a noun phrase like 一个队, you normally need 是:

• 我们是一个队。 = correct

Without 是, the sentence does not sound like standard complete Mandarin.

队 means something like team, squad, or group, depending on context.

Common meanings include:

• a sports team
• a work team
• a squad or unit
• a line of people in some contexts

In 我们是一个队, the meaning is team: a group acting together as one unit.

For beginner Chinese, 个 is perfectly fine and very common because it is the most general measure word.

Native speakers may also use more specific expressions in some contexts, but 一个队 is natural and easy to understand.

So for a learner, this is a good sentence pattern to remember.

Because this sentence follows a very basic Chinese pattern:

Subject + 是 + noun phrase

So:

• 我们 = we
• 是 = are
• 一个队 = a team

This happens to match English quite closely:

We + are + a team

Not every Chinese sentence lines up this neatly with English, but this one does.

我们 means we/us in a general sense.

咱们 also means we/us, but it often includes the listener more explicitly, like we all, including you.

So:

• 我们是一个队。 = We are a team.
• 咱们是一个队。 = We’re on the same team / We’re one team, including you.

If you are speaking to someone you want to include, 咱们 can work well. But 我们 is the more basic and widely taught form.

A natural pronunciation is:

Wǒmen shì yí ge duì.

A few notes:

• 我们 is often pronounced wǒmen, with men light and unstressed.
• 是 is shì with a clear fourth tone.
• 一 becomes yí here.
• 个 is often light in natural speech: ge
• 队 is duì with a fourth tone.

So in connected speech, it often sounds close to:

wǒmen shì yí ge duì

Yes, it often can.

Besides simply meaning we are a team, it can also suggest:

• unity
• cooperation
• solidarity
• we’re in this together

So depending on context, it may sound encouraging or motivational, not just descriptive.