wàimiàn zhème lěng, wǒmen bùrú zài jiā kàn diànyǐng ba.

外面 means outside or outdoors. Putting it first sets the scene/topic: as for outside / outside, it’s so cold.

So:

• 外面这么冷 = It’s so cold outside
• literally: Outside is this cold

Chinese often starts with the place or topic before commenting on it.

In Mandarin, adjectives can act like predicates by themselves, so you usually do not need a word like is before them.

So:

• 外面冷 = Outside is cold
• not 外面是冷

This is very normal in Chinese. Adjectives often function more like stative verbs.

这么 means so, this, or this much, depending on context. Before an adjective, it often means so.

Here:

• 这么冷 = so cold

It emphasizes the degree of coldness. Very common pattern:

• 这么大 = so big
• 这么快 = so fast
• 这么晚 = so late

They are not the same.

• 很冷 = cold / quite cold
• 这么冷 = so cold

很 is often just a normal linking adverb before an adjective, while 这么 points to a noticeable degree.

So:

• 外面很冷 = It’s cold outside
• 外面这么冷 = It’s so cold outside

The second one sounds more like the speaker is reacting to the situation.

不如 literally means not as good as, but in many everyday sentences it works like might as well or why don’t we...

Here:

• 我们不如在家看电影吧 = Why don’t we just stay home and watch a movie? = We might as well watch a movie at home.

It introduces a suggestion, especially when one option seems better than another in the situation.

Not always. It can be used in two common ways:

1. Direct comparison

   • 我不如他高。
   • I’m not as tall as him.

2. Suggestion

   • 我们不如早点走吧。
   • Why don’t we leave early?

In your sentence, it is the suggestion use.

Chinese usually puts location phrases before the main verb.

So the order is:

• 在家 = at home
• 看电影 = watch a movie / watch movies

Combined:

• 在家看电影 = watch a movie at home

This follows a very common word order:

Subject + location + verb + object

For example:

• 我在学校学习。 = I study at school.
• 他们在饭馆吃饭。 = They eat at a restaurant.

Because 在家 means at home, describing location, not movement.

• 在家 = at home
• 回家 = go home / return home

In this sentence, the idea is not go home and watch a movie, but watch a movie at home. So 在家 is the correct choice.

It can mean either, depending on context.

• 看电影 literally = watch movie(s)

Chinese nouns often do not show singular/plural the way English does. So this could mean:

• watch a movie
• watch movies
• go see a movie

In this sentence, English usually renders it as watch a movie or watch movies at home, depending on the translator’s style.

吧 softens the sentence and makes it sound like a suggestion, proposal, or gentle recommendation.

So:

• 我们不如在家看电影。 = more plain, possibly incomplete-sounding in conversation
• 我们不如在家看电影吧。 = Why don’t we watch a movie at home?

It makes the tone more natural and less forceful.

No, it’s very natural.

• 不如 already suggests a better idea
• 吧 makes the suggestion softer and more conversational

Together they sound very idiomatic:

• 我们不如在家看电影吧。

This is a very common way to make a friendly suggestion.

我们 means we, and it makes clear that the suggestion includes the speaker and at least one other person.

You could sometimes omit it if the context is obvious, but keeping it makes the sentence clearer and more natural:

• 我们不如在家看电影吧。 = Why don’t we watch a movie at home?

Without 我们, it might sound less complete unless the conversation already makes the subject obvious.

The sentence has two parts:

1. 外面这么冷

   • situation/reason: It’s so cold outside

2. 我们不如在家看电影吧

   • suggestion/result: Why don’t we watch a movie at home?

So the full logic is:

Since it’s so cold outside, why don’t we watch a movie at home?

This kind of situation first, suggestion second structure is very common in Mandarin.

Yes. For example:

• 外面太冷了，我们不如在家看电影吧。

That also sounds natural.

The difference is roughly:

• 这么冷 = so cold
• 太冷了 = too cold / really cold

太冷了 often sounds a bit more emotional or emphatic. 这么冷 sounds slightly more like pointing out the degree of coldness in the current situation.

Very roughly, it is:

• 外面 = outside
• 这么 = so
• 冷 = cold
• 我们 = we
• 不如 = might as well / why don’t
• 在家 = at home
• 看电影 = watch a movie
• 吧 = suggestion particle

So a very literal version would be:

Outside so cold, we might as well at home watch a movie, okay?

That is not natural English, but it helps show how Mandarin builds the sentence.