Over the centuries, Celtic languages gradually retreated as Latin and later Germanic languages spread across Europe. Today, Celtic languages survive only in parts of France and the British Isles.

They are divided into two main branches:

• Goidelic (Gaelic): Irish, Scottish Gaelic, and Manx

• Brythonic: Welsh, Cornish, and Breton.

Some Celtic languages have already disappeared:

-Cornish became extinct in the 18th century

-Manx died out as a native language after World War II.

Most Celtic languages are now spoken by minority groups of people and face competition from dominant languages such as English and French.

-Scottish Gaelic survives mainly in the Highlands of Scotland

-Welsh and Irish are still spoken, but many speakers are bilingual.

Some of these people settled in the area that is now Iran, while others continued their migration into India. Later movements spread Iranian languages into distant regions, including southern Russia and central China.

The earliest evidence of Iranian languages can be divided into two groups: Eastern Iranian and Western Iranian. The most important ancient languages are Avestan and Old Persian.

Avestan

Avestan is the language of the Avesta, the sacred book of the Zoroastrians. It is sometimes called Zend. The Avesta consists of two main parts:

1. The Gathas – metrical sermons attributed to Zoroaster, dating back to about 1000 BC.

2. The Avesta proper – a collection of hymns, legends, prayers, and legal texts composed several centuries later.

Old Persian

Old Persian is known mainly through inscriptions that record the achievements and conquests of Darius I and Xerxes I. One of the most famous inscriptions is found at Behistun Inscription, where texts were carved into a mountainside using cuneiform writing.

Later, Old Persian developed into Middle Iranian, also known as Pahlavi. Pahlavi was the official language of the state and the Zoroastrian Church during the Sasanian Empire. It is the ancestor of modern Persian (Farsi), which has been an important language of culture and literature since the ninth century.

Modern Persian contains many words borrowed from Arabic. As a result, its vocabulary includes a significant amount of Arabic influence, even though it remains an Iranian language.

The Baltic group consists of three languages: Prussian, Latvian, and Lithuanian. Prussian became extinct after being replaced by German in the seventeenth century. In the present, Latvian is spoken in Latvia, while Lithuanian is spoken in Lithuania. Lithuanian is especially significant because it has preserved many ancient features that have disappeared from most other Indo-European languages. The Slavic languages were once very similar and remained closely connected until around the seventh or eighth century.

Nowadays they're now divided into three groups: East Slavic, West Slavic, and South Slavic. The earliest recorded Slavic language is found in religious texts translated by the missionaries Cyril and Methodius in the ninth century. This language, known as Old Church Slavonic, was used for centuries by the Orthodox Church.

The East Slavic group includes Russian, Belorussian, and Ukrainian. West Slavic includes Polish, Czech, Slovak, and Sorbian. The South Slavic group consists of Bulgarian, Serbo-Croatian, Slovene, and Macedonian. Together, these languages are spoken across a large part of Eastern and Southeastern Europe.

Overall, the Slavic languages have remained relatively homogeneous and preserve many features of their common origin. In addition, the Baltic and Slavic peoples lived in close contact for many centuries after separating from the original Indo-European community, which helps explain the similarities that still exist between their languages today.  

• East Germanic

• North Germanic

• West Germanic

East Germanic

The most important East Germanic language was Gothic. In the 4th century, Ulfilas translated parts of the Bible into Gothic, providing the earliest extensive record of a Germanic language. Gothic later disappeared, along with other East Germanic languages such as Burgundian and Vandalic.

North Germanic

North Germanic languages developed in Scandinavia. Their earliest form was Old Norse, the language of the Vikings. Over time, it evolved into:

• Swedish

• Danish

• Norwegian

• Icelandic

Old Icelandic is famous for its rich literature, including the Poetic Edda, the Prose Edda, and the Icelandic sagas.

West Germanic

West Germanic is the branch that includes English. Around the 7th century, it divided into Low German and High German.

Low German languages included Old English, Old Frisian, Old Saxon, and Old Low Franconian. These languages later developed into modern English, Frisian, Dutch, Flemish, and Low German.

High German became the basis of modern German and eventually the literary language of Germany.

The oldest major literary monuments of the language are Homer’s Iliad and Odyssey (8th century B.C.). Historically, the Greek language was divided into five main dialect groups:

• Ionic: Located in Asia Minor and the Aegean islands (includes the Attic subdialect).

• Aeolic: Spoken in the north and northeast.

• Arcadian-Cyprian: Found in the Peloponnesus and Cyprus.

• Doric: Replaced Arcadian in the Peloponnesus.

• Northwest Greek: Spoken in north-central and western mainland Greece.

Attic (Koiné)

(The dialect of Athens) it became dominant due to Athens' political, commercial, and cultural supremacy during the Golden Age of Pericles (5th century B.C.) and the era of its great philosophers, playwrights, and historians.

Because of this, Attic evolved into the Koiné (common Greek), which eventually replaced the other ancient dialects. The conquests of Alexander the Great (4th century B.C.) spread this Koiné across the eastern Mediterranean (Egypt, Syria, Mesopotamia, and Asia Minor) as an international language. It later became the language of the New Testament and Byzantine literature.

Modern Greek

Modern Greek dialects developed from local variations of the Koiné over the centuries. Historically, two forms of the language existed in Greece:

• Demotic (Popular): The natural, everyday spoken language of the people.

• "Pure" (Katharevousa): A conscious, artificial effort to restore ancient Greek vocabulary and inflections.

While both forms have played a role in education, Demotic holds the current official position in Greece.