Turkmen

Closely related, not the same. Both are Oghuz Turkic — the same major branch — and share grammatical structure and many cognates. A Turkish speaker can understand significant portions of spoken or written Turkmen with effort, and vice versa. The languages have diverged enough through separate history (Ottoman/Turkish vs Central Asian Turkmen) that fluency in one doesn't fully transfer to the other without study.

Turkmenistan as the official language, with around 4 million native speakers there. Substantial Turkmen communities also live in northern Iran, northwestern Afghanistan, Iraq (Iraqi Turkmen, around the Tal Afar and Kirkuk regions), Syria, and Russia. The Turkmen diaspora extends to Turkey and the broader post-Soviet space.

Originally Perso-Arabic (until the 1920s), briefly a first Latin alphabet (1928–1940), then Cyrillic under the Soviet Union (1940–1993), then back to a new Latin alphabet that has been revised several times since. The current Latin alphabet uses extra letters and diacritics for Turkmen-specific sounds. Older publications and many older readers still use Cyrillic.

Agglutinative like other Turkic languages, with vowel harmony, no grammatical gender, SOV word order, and verbs that conjugate for person, number, tense, mood, aspect, and (in some forms) evidentiality. Turkmen preserves vowel harmony more fully than Uzbek (which lost it through Persian contact) and behaves grammatically in ways closer to Turkish and Azerbaijani.

Not by family — Turkmen is Turkic, Persian is Iranian (Indo-European). The two have been in long contact, particularly along the historical Silk Road and through Iranian Turkmenistan, leaving Persian loanwords in Turkmen vocabulary. Grammatically the languages remain distinct, with Persian non-agglutinative SOV and Turkmen full-agglutinative SOV with vowel harmony.