Min fot är kall efter regnet.

Because fot is a common gender noun in Swedish (an en-word): en fot.

For en-words, the possessive is min:

• min fot = my foot

For ett-words, you use mitt:

• mitt hus = my house

So:

• en fot → min fot
• not mitt fot

In Swedish, when you use a possessive like min, din, hans, hennes, and so on, you normally do not add an article.

So you say:

• min fot = my foot

Not:

• min en fot
• min foten

This works much like English, where we say my foot, not the my foot.

The adjective must agree with the noun it describes.

Here, fot is an en-word and it is singular, so the basic adjective form is used:

• en kall fot = a cold foot
• Min fot är kall = my foot is cold

Compare:

• ett kallt rum = a cold room
• Mina fötter är kalla = my feet are cold

So:

• singular en-word → kall
• singular ett-word → kallt
• plural → kalla

Är is the present tense of vara, which means to be.

So:

• är = is / are / am, depending on context

In this sentence:

• Min fot är kall = My foot is cold

Swedish verbs do not change depending on the subject the way English verbs do. The form är stays the same:

• jag är
• du är
• han är
• vi är

Efter is a preposition meaning after.

Regnet is the definite form of regn:

• ett regn = a rain
• regnet = the rain

So:

• efter regnet = after the rain

This phrase tells you when or under what circumstances the foot is cold.

Because the sentence is referring to the rain, not rain in a general sense.

• regn = rain, as a general substance or phenomenon
• regnet = the rain, a specific rain event

So:

• efter regnet = after the rain

If you said efter regn, it would sound less natural in this sentence. Swedish usually prefers the definite form here when talking about a specific rain that just happened.

Yes, fot is singular here, but it is in its indefinite form because it is preceded by min.

Compare:

• fot = foot
• foten = the foot
• min fot = my foot

In Swedish, possessives usually replace the definite article idea:

• foten = the foot
• min fot = my foot

So min fot is exactly what you want here.

Yes, that is perfectly possible.

Both of these are natural:

• Min fot är kall efter regnet.
• Efter regnet är min fot kall.

When a sentence starts with a time phrase like Efter regnet, Swedish uses normal V2 word order, meaning the verb comes second:

• Efter regnet är min fot kall

You do not say:

• Efter regnet min fot är kall

Swedish can absolutely describe a body part directly with an adjective:

• Min fot är kall = My foot is cold

This is normal and natural.

Swedish also often talks about body parts in similar ways:

• Mina händer är kalla = My hands are cold
• Min näsa är kall = My nose is cold

So this sentence is grammatically straightforward and idiomatic.

The plural of fot is fötter.

So the sentence becomes:

• Mina fötter är kalla efter regnet.

Notice the changes:

• min → mina for plural
• fot → fötter
• kall → kalla for plural agreement

So:

• Min fot är kall = My foot is cold
• Mina fötter är kalla = My feet are cold

Unfortunately, there is no perfect rule that lets you always predict noun gender in Swedish. In many cases, you simply learn the noun together with its article:

• en fot
• ett regn

That is why Swedish learners are usually encouraged to memorize nouns with en or ett from the beginning.

In this sentence, knowing the gender helps you choose:

• min because fot is an en-word
• kall because it agrees with an en-word singular noun

Only if you mean leg, not foot.

In Swedish:

• fot = foot
• ben = leg

So:

• Min fot är kall = My foot is cold
• Mitt ben är kallt = My leg is cold

Notice that ben is an ett-word, so it takes:

• mitt ben
• kallt

That makes it a useful comparison with the original sentence.