Πλένω τα μαλλιά μου κάθε δύο μέρες.

Because Greek verb endings usually already show the subject.

• πλένω = I wash
• The ending -ω tells you it is 1st person singular.

So Greek often leaves out the subject pronoun unless it needs emphasis or contrast.

• Πλένω τα μαλλιά μου. = I wash my hair.
• Εγώ πλένω τα μαλλιά μου. = I wash my hair. (with extra emphasis)

Yes, in a grammatical sense, Greek usually treats hair on the head as plural:

• το μαλλί = a hair / wool / a strand in some contexts
• τα μαλλιά = hair (as a whole, on someone’s head)

So τα μαλλιά μου literally looks like my hairs, but the natural English translation is simply my hair.

This is very normal in Greek. A learner should think:

• τα μαλλιά μου = my hair

not as strange or incorrect, just as a different way the language organizes the idea.

Greek normally uses the definite article with body parts and with many possessed nouns.

So:

• τα μαλλιά μου = literally the hair of me / my hair

This is one of the most common Greek patterns:

• το χέρι μου = my hand
• τα μάτια μου = my eyes
• το σπίτι μου = my house

In English, we do not usually say the hair my, but in Greek the article is very natural and usually expected.

Because Greek possessive weak pronouns like μου, σου, του, της often come after the noun.

So:

• τα μαλλιά μου = my hair
• το βιβλίο μου = my book
• η φίλη μου = my friend

A very useful pattern is:

• article + noun + possessive pronoun

So here:

• τα = the
• μαλλιά = hair
• μου = my

It is in the accusative case, because it is the direct object of πλένω.

Breakdown:

• πλένω = I wash
• what do I wash? → τα μαλλιά μου

The form τα μαλλιά is the same for nominative plural and accusative plural in this neuter noun, so the article alone does not visibly change here. But syntactically it is the object, so it is accusative.

It means every two days.

Word by word:

• κάθε = every / each
• δύο = two
• μέρες = days

So the full sentence means:

• I wash my hair every two days.

In everyday English, this may sometimes overlap with every other day, though the phrasing is not always identical in every context.

Often, yes, in everyday use it can be very close.

But learners should know a few Greek ways to express this idea:

• κάθε δύο μέρες = every two days
• κάθε δεύτερη μέρα = every second day
• μέρα παρά μέρα = every other day

All of these can be used depending on style and context.
In your sentence, κάθε δύο μέρες is a very straightforward and natural way to say it.

Because μέρα is the common everyday shortened form of ημέρα.

Both are related:

• η ημέρα = the day
• η μέρα = the day

In modern spoken Greek, μέρα / μέρες is extremely common and natural.

So:

• κάθε δύο μέρες sounds very normal in everyday language.

It is correct, but Greek also very commonly uses λούζω for washing hair.

Compare:

• Πλένω τα μαλλιά μου. = I wash my hair.
• Λούζω τα μαλλιά μου. = I wash my hair.
• Λούζομαι. = I wash my hair / I shampoo my hair.

So πλένω is a general verb meaning wash, while λούζω is especially associated with washing hair.

Yes, but the structure changes depending on the verb.

With πλένω, Greek commonly says:

• Πλένω τα μαλλιά μου.

With λούζω, Greek often uses the middle/passive form:

• Λούζομαι. = I wash my hair.
• Λούζομαι κάθε δύο μέρες. = I wash my hair every two days.

So Greek does not always use a reflexive structure exactly the same way English does. Very often, a simple verb plus the possessed body part is enough.

Yes. Greek word order is more flexible than English.

Your sentence:

• Πλένω τα μαλλιά μου κάθε δύο μέρες.

A very natural variation is:

• Κάθε δύο μέρες πλένω τα μαλλιά μου.

Both mean the same thing. The difference is mainly one of emphasis or rhythm:

• starting with Πλένω focuses first on the action
• starting with Κάθε δύο μέρες highlights the frequency

A simple pronunciation guide would be:

• Πλένω → PLEH-no
• τα → ta
• μαλλιά → ma-LYA
• μου → moo
• κάθε → KA-the
• δύο → THEE-o
• μέρες → MEH-res

Putting it together:

• PLEH-no ta ma-LYA moo KA-the THEE-o MEH-res

A couple of useful notes:

• λλι in μαλλιά sounds like lya
• δ in modern Greek sounds like th in this
• the stress matters: Πλένω, μαλλιά, κάθε, μέρες

Here is the sentence piece by piece:

• Πλένω = I wash
• τα μαλλιά μου = my hair
• κάθε δύο μέρες = every two days

More technically:

• Πλένω: 1st person singular, present tense
• τα μαλλιά: neuter plural direct object
• μου: weak possessive pronoun, meaning my
• κάθε δύο μέρες: adverbial time expression showing frequency

So the overall structure is:

• verb + object + time expression

Normally, no. That does not sound natural in standard Greek.

The natural order is:

• Πλένω τα μαλλιά μου.

The possessive pronoun μου usually follows the noun phrase it belongs to:

• το πρόσωπό μου = my face
• τα χέρια μου = my hands
• τα μαλλιά μου = my hair

So for learners, the safest pattern is:

• article + noun + μου

Because κάθε is generally indeclinable in modern Greek. It does not change for gender, number, or case.

So you get:

• κάθε μέρα = every day
• κάθε δύο μέρες = every two days
• κάθε εβδομάδα = every week
• κάθε χρόνο = every year

That makes it a very useful and easy word to learn.