Adaptarea este dificilă.

Because Romanian usually puts the definite article at the end of the noun, not before it.

• adaptare = adaptation / an adaptation
• adaptarea = the adaptation

So adaptarea is the definite form of the noun.

Romanian has a postposed definite article, which means the article is added to the end of the noun.

This is a very important feature of Romanian grammar:

• băiat = boy
• băiatul = the boy
• fată = girl
• fata = the girl
• adaptare = adaptation
• adaptarea = the adaptation

So adaptarea is completely normal Romanian structure.

Romanian often uses the definite article with abstract nouns in places where English may use no article at all.

So adaptarea este dificilă can, depending on context, correspond to:

• Adaptation is difficult
• The adaptation is difficult

In Romanian, abstract ideas like life, love, education, adaptation, and so on are often expressed with the definite form more naturally than in English.

Este is the 3rd person singular present of the verb a fi = to be.

So here it means is.

A few present-tense forms of a fi are:

• eu sunt = I am
• tu ești = you are
• el/ea este = he/she is
• noi suntem = we are
• voi sunteți = you are
• ei/ele sunt = they are

In this sentence, adaptarea is singular, so este is the correct form.

Yes. E is a very common short form of este.

So both are correct:

• Adaptarea este dificilă.
• Adaptarea e dificilă.

The version with e is very common in everyday speech and informal writing. The version with este sounds a bit fuller or more formal.

Because the adjective has to agree with the noun.

Adaptarea is a feminine singular noun, so the adjective must also be feminine singular:

• masculine singular: dificil
• feminine singular: dificilă
• masculine plural: dificili
• feminine plural: dificile

So:

• un examen dificil = a difficult exam
• o situație dificilă = a difficult situation

Since adaptarea is feminine singular, dificilă is the correct form.

Yes. In Romanian, adjectives agree with the noun whether they come:

• directly next to the noun, or
• after a verb like a fi

So both of these show agreement:

• adaptarea dificilă = the difficult adaptation
• adaptarea este dificilă = the adaptation is difficult

English does not change difficult, but Romanian does.

Adaptare is a feminine noun.

You can see that in the sentence because:

• it takes the feminine definite form adaptarea
• it uses the feminine adjective dificilă

Many Romanian nouns ending in -are are feminine, especially abstract nouns formed from verbs.

It is in the nominative, because it is the subject of the sentence.

In Adaptarea este dificilă, the structure is:

• Adaptarea = subject
• este = verb
• dificilă = predicate adjective

For this noun, the nominative and accusative forms are the same, so the form itself does not change here.

The neutral, most natural order is:

• Adaptarea este dificilă.

Romanian word order is somewhat flexible, so other orders are possible for emphasis, but they are more marked. For example:

• Dificilă este adaptarea.

That sounds more emphatic or literary, something like It is adaptation that is difficult or Difficult is the adaptation.

For a learner, the normal pattern subject + este + adjective is the safest choice.

A rough English-friendly pronunciation is:

ah-dap-TA-re-a YES-te dee-fee-CHEE-luh

A few helpful details:

• ă is a short central vowel, somewhat like the a in sofa
• ci in dificilă sounds like chee
• este often sounds like YES-te

You do not need to make it sound exactly like English spelling suggests; Romanian pronunciation is usually more regular than English.

Yes, but it means something different.

• Adaptarea este dificilă = the adaptation / adaptation is difficult
• O adaptare este dificilă = an adaptation is difficult

Using o makes it indefinite and often sounds more specific or less general. The original sentence sounds more natural for a general statement or for referring to a known adaptation.

It is basically neutral standard Romanian.

• Adaptarea este dificilă sounds normal and correct in standard Romanian.
• Adaptarea e dificilă is a little more conversational.

So the sentence is perfectly natural for learners to use.