Learn Hardcore Greek: Τα ελληνικά είναι δύσκολη γλώσσα.

So even though the meaning is singular (“Greek” as one language), the grammar is neuter plural. That’s why you see τα (plural “the”) and ελληνικά in plural form.

What are the gender, number, and case of each word in Τα ελληνικά είναι δύσκολη γλώσσα?

Τα – definite article, neuter plural nominative
ελληνικά – adjective used as a noun, neuter plural nominative (from ελληνικός, -ή, -ό = Greek)
είναι – 3rd person singular/plural, present tense of είμαι (to be)
δύσκολη – adjective, feminine singular nominative (from δύσκολος, -η, -ο = difficult)
γλώσσα – noun, feminine singular nominative (“language, tongue”)

Subject: Τα ελληνικά
Verb: είναι
Predicate (complement): δύσκολη γλώσσα

Why is it «δύσκολη γλώσσα» and not «δύσκολο» or «δύσκολα»?

The adjective must agree with the noun it describes, which here is γλώσσα:

γλώσσα is feminine, singular, nominative.
So the adjective must be feminine singular nominative → δύσκολη.

Some contrasts:

δύσκολη γλώσσα = difficult language (γλώσσα is feminine → δύσκολη)
δύσκολο μάθημα = difficult lesson (μάθημα is neuter → δύσκολο)
δύσκολος άνθρωπος = difficult person (masculine → δύσκολος)

If you said «Τα ελληνικά είναι δύσκολα», then δύσκολα is neuter plural agreeing with τα ελληνικά. That creates a different nuance (see next question).

What’s the difference between «Τα ελληνικά είναι δύσκολη γλώσσα» and «Τα ελληνικά είναι δύσκολα»?

Τα ελληνικά είναι δύσκολη γλώσσα.
Literally: “Greek is a difficult language.”
You are explicitly classifying Greek as a language and describing that language as difficult.
Τα ελληνικά είναι δύσκολα.
Literally: “Greek is difficult.”
Here δύσκολα agrees with τα ελληνικά (neuter plural), so you’re saying that (the) Greek (language) is difficult in general, without mentioning the word “language”.

Both are natural. The first one sounds a bit more explicit and “schoolbook-like”; the second is shorter and very common in speech.

Why does «δύσκολη γλώσσα» agree with γλώσσα and not with τα ελληνικά?

In this sentence, «δύσκολη γλώσσα» is a predicate noun phrase telling you what Greek is:

Subject: Τα ελληνικά
Verb: είναι
Predicate: (μια) δύσκολη γλώσσα

Inside that predicate phrase, the adjective δύσκολη must agree with the head noun γλώσσα, not with the subject.

So agreement works inside each noun phrase:

η δύσκολη γλώσσα (fem. sg.)
τα δύσκολα μαθήματα (neut. pl.)

The verb είναι simply links subject and predicate; it doesn’t force adjectives in the predicate to agree with the subject’s gender/number when they belong to a different noun like γλώσσα.

Can I leave out «γλώσσα» and just say «Τα ελληνικά είναι δύσκολη»?

No, «Τα ελληνικά είναι δύσκολη» is wrong, because δύσκολη is feminine singular but there is no feminine noun there for it to agree with.

You can say either:

Τα ελληνικά είναι δύσκολα. (adjective agrees with τα ελληνικά)
Τα ελληνικά είναι (μια) δύσκολη γλώσσα. (adjective agrees with γλώσσα)

But if you want to omit γλώσσα, the adjective must now agree with τα ελληνικά, so it has to be δύσκολα, not δύσκολη.

Why is there no indefinite article (a) before «δύσκολη γλώσσα»? Can I say «είναι μια δύσκολη γλώσσα»?

Both are possible:

Τα ελληνικά είναι δύσκολη γλώσσα.
Τα ελληνικά είναι μια δύσκολη γλώσσα.

In Greek, the indefinite article (ένας, μια/μία, ένα) is often optional in sentences with είμαι that classify something:

Είμαι (ένας) φοιτητής. = I am a student.
Είναι (μια) δύσκολη γλώσσα. = It is a difficult language.

Leaving out μια is very common, especially in more general, descriptive statements.
Including μια can sound a bit more individual / specific, but here the difference is small and both are natural.

Can I change the word order? For example, «Η ελληνική γλώσσα είναι δύσκολη» or «Δύσκολη γλώσσα είναι τα ελληνικά»?

Yes. Greek word order is flexible, especially with the verb είμαι. Some natural variants:

Τα ελληνικά είναι δύσκολη γλώσσα.
Η ελληνική γλώσσα είναι δύσκολη.
- Here you make «η ελληνική γλώσσα» the subject. The adjective ελληνική now agrees with γλώσσα (feminine).
Δύσκολη γλώσσα είναι τα ελληνικά.
- More emphatic: “A difficult language, that’s Greek.”

All three are grammatical; the differences are in emphasis and style, not in basic correctness.

How do you pronounce Τα ελληνικά είναι δύσκολη γλώσσα?

One simple phonetic guide (stress in CAPS):

Τα → “ta” (like tah)
ελληνικά → “eh-lee-nee-KA”
είναι → “EE-neh”
δύσκολη → “THEES-ko-lee” (th as in this)
γλώσσα → “GLO-sa” (smooth g+l together; the ω just lengthens the ‘o’ sound; double σ is just a long s)

Full sentence:
ta eh-lee-nee-KA EE-neh THEES-ko-lee GLO-sa

Main stresses: ελληνικά, δύσκολη, γλώσσα each have one stressed syllable marked by the written accent (´).

Why is «ελληνικά» written with a lowercase initial, not «Ελληνικά»?

In Greek:

Nationalities as nouns referring to people are capitalized:
- ο Έλληνας (a Greek man), η Ελληνίδα (a Greek woman), οι Έλληνες (Greeks)
Adjectives for nationality and the names of languages are usually lowercase:
- η ελληνική μουσική = Greek music
- τα ελληνικά = Greek (language)
- τα αγγλικά = English

So ελληνικά here is the language, so it’s correctly written with a lowercase initial.

What form of the verb is «είναι» and could it be left out?

Είναι is the present tense of είμαι (to be), 3rd person singular and plural (same form for both):

αυτός / αυτή / αυτό είναι = he / she / it is
αυτοί / αυτές / αυτά είναι = they are

In standard sentences like this, you must include είναι:

Τα ελληνικά είναι δύσκολη γλώσσα. ✔
Τα ελληνικά δύσκολη γλώσσα. ✘ (sounds like a telegram or a newspaper headline)

Omitting είναι sometimes happens in headlines, slogans, or very informal speech for stylistic effect, but in normal grammar, you keep it.