Philologically Turkish belongs to the so called Altaic languages which still is controversial. The Altaic languages with its origin in the central Asian Altai mountains are divided into

– Turkic languages
– Mongolian languages
– Tungusian languages 

Summarizing the Turkic languages which are spoken in Turkey, Azerbaijan, Kazakhstan, Kirghizia, Uzbekistan, Turkmenistan until China at the Uighurs they globally form the seventh biggest language family. Depending on the sources there are currently between 160 to 400 millions Turkic language speakers.

Turkish, as the language spoken in modern Turkey, belongs to the concrete branch of Oghuzian and is with its 80 millions speakers the most important language of this branch. The very related Azerbaijanian takes with 30 millions speakers the second rank. Apart from those there are less known languages like Turkmenian, Khorazan Turkish, Afshagarian and others.
It is said that the Turkic languages are also related to Hungarian and Finnish (finno-ugric languages) and partly also to American natives languages. This is traced back to the fact that these languages also use agglutinating word particles (syllables which are added to words in order to form complete sentences) and vowel harmonies. But among experts this cognation is extremely controversial.

But in fact there is an extensive possibility to communicate as a Turkey Turk with others Turkic language speakers of the above mentioned regions. You can find here an interesting page in order to compare words of the different Turkic languages:
Türk Lehçeleri Sözlüğü – this website is in Turkish. Between the pop-up menu and the search field (“Araştır”) there is an almost invisible space for typing in any word which then is shown in different Turkic languages.

In Turkey at least 90% of the population speak Turkish and the Istanbul vernacular is the most spoken dialect. Next to Turkish there exist other old minority languages which are not of Turkic origin such as Kurdish, Arabic, Armenian, Greek, Lazian, Cherkess and others.
During the age of the Ottoman Empire (14th to 20th century) the Ottoman Turkish as antecessor of modern Turkish was influenced by Arabic and partly Persian which is noticeable until nowadays. But anyway there is no cognation between these languages. Turkish used to be written with Arabic letters but it was never sufficient expressing the special Turkish sounds.After the breakdown of the Ottoman Empire 1923 the laicists took power under the leadership of Mustafa Kemal Atatürk, the founder of the nowadays Turkey and introduced in 1928 a language reform. From then on Turkish was written with latin alphabet. Furthermore an initiative has been started to replace foreign words – mostly Arabic – by turkish words. Among others this also affected and still affects French, English and Italian origin terms. This initiative is still going on and is operated by Türk Dili Kurumu, the “Institute for Turkish Language”.