Τελευταία πίνω λιγότερο καφέ γιατί δεν κοιμάμαι καλά.

Here Τελευταία means lately / recently / these days.

Even though it looks like the feminine form of an adjective, in this expression it is being used adverbially. Greek very often uses τελευταία at the beginning of a sentence to mean recently:

• Τελευταία δουλεύω πολύ. = Lately I’ve been working a lot.
• Τελευταία δεν βγαίνω πολύ. = Lately I don’t go out much.

So in this sentence, Τελευταία sets the time frame for the whole statement.

Greek often uses the present tense for actions or habits that are true these days / lately / in the current period.

So πίνω λιγότερο καφέ literally means I drink less coffee, but in natural English the best translation is often:

• I’ve been drinking less coffee lately
• Lately I’m drinking less coffee

This is a normal difference between Greek and English. Greek present tense can cover what English sometimes expresses with a present perfect continuous idea.

Because καφέ is the accusative singular form, and it is the direct object of πίνω.

The dictionary form is:

• ο καφές = coffee / the coffee

But after a verb like πίνω you need the accusative:

• πίνω καφέ = I drink coffee
• πίνω τον καφέ μου = I drink my coffee

So:

• nominative: ο καφές
• accusative: τον καφέ / καφέ

Because λιγότερο here means less, and it is being used with coffee as an uncountable substance.

So λιγότερο καφέ = less coffee

This is different from talking about countable items. For example:

• πίνω λιγότερο καφέ = I drink less coffee
• πίνω λιγότερους καφέδες = I drink fewer coffees / fewer cups of coffee

So in your sentence, the speaker is talking about the amount of coffee in general, not the number of individual coffees.

In Greek, as in English, you often leave out the article with substances or general, indefinite amounts:

• πίνω καφέ = I drink coffee
• πίνω νερό = I drink water

If you add an article, it usually becomes more specific:

• πίνω τον καφέ μου = I’m drinking my coffee
• πίνω τον καφέ που έφτιαξες = I’m drinking the coffee you made

So λιγότερο καφέ means less coffee in a general sense.

Yes, γιατί can mean both because and why.

The meaning depends on context, punctuation, and intonation:

• Γιατί δεν κοιμάσαι; = Why aren’t you sleeping?
• Δεν πίνω καφέ γιατί δεν κοιμάμαι καλά. = I don’t drink coffee because I don’t sleep well.

In your sentence, γιατί clearly introduces the reason, so it means because.

A more formal or explicit alternative would be επειδή, but γιατί is extremely common in everyday Greek.

Δεν is the basic negation word used before verbs in Greek. It means not.

Here:

• δεν κοιμάμαι καλά = I do not sleep well

A few key points:

• δεν normally comes right before the verb
• it negates the verb phrase
• in speech it is unstressed and closely attached to the verb

Compare:

• κοιμάμαι καλά = I sleep well
• δεν κοιμάμαι καλά = I don’t sleep well

Because κοιμάμαι is the normal modern Greek verb meaning I sleep / I am sleeping.

This is one of those Greek verbs that appears in the middle/passive-looking form but has an active meaning in English. So you simply learn it as:

• κοιμάμαι = I sleep
• κοιμάσαι = you sleep
• κοιμάται = he/she sleeps

In other words, this is just the standard form of the verb in modern Greek.

Because καλά is functioning as an adverb, meaning well.

It describes how the person sleeps:

• κοιμάμαι καλά = I sleep well

This is very common in Greek: the neuter plural form of an adjective is often used adverbially.

Compare:

• καλός άνθρωπος = a good person
• καλό παιδί = a good child
• μιλάει καλά = he/she speaks well
• κοιμάμαι καλά = I sleep well

So here καλά does not mean good; it means well.

Greek word order is fairly flexible, although some orders sound more natural than others.

Your sentence is very natural:

• Τελευταία πίνω λιγότερο καφέ γιατί δεν κοιμάμαι καλά.

But other versions are also possible, with slightly different emphasis:

• Πίνω τελευταία λιγότερο καφέ γιατί δεν κοιμάμαι καλά.
• Γιατί δεν κοιμάμαι καλά, τελευταία πίνω λιγότερο καφέ.

Putting Τελευταία first is very common because it immediately sets the time frame: lately.

It breaks down like this:

• Τελευταία = lately / recently
• πίνω = I drink / I’ve been drinking
• λιγότερο καφέ = less coffee
• γιατί = because
• δεν κοιμάμαι καλά = I don’t sleep well

So the structure is:

time expression + main clause + reason clause

That makes it easy to understand as:

Lately, I drink less coffee because I don’t sleep well.

In natural English, that often becomes:

Lately I’ve been drinking less coffee because I’m not sleeping well.