About the Azerbaijani language 
It gradually supplanted the previous Iranian languages — Tat, Azari, and Middle Persian in northern Iran, and a variety of Caucasian languages in the Caucasus, particularly Udi, and had become the dominant language before by the time of the Safavid dynasty; however, minorities in both the Republic of Azerbaijan and Iran continue to speak the earlier Iranian languages to this day, and both Middle and New Persian loanwords are numerous in Azerbaijani.
The historical development of Azerbaijani can be divided into two major periods: early (ca. 16th to 18th century) and modern (18th century to present). Old Azerbaijani differs from its descendant in that it contained a much greater amount of Persian, Arabic, and Ottoman Turkish loanwords, phrases and syntactic elements. Early writings in Azerbaijani also demonstrate lingustic interchangeability between Oghuz and Kypchak elements in many aspects (such as pronouns, case endings, participles, etc...). As Azerbaijani gradually moved from being merely a language of epic and lyric poetry to being also a language of journalism and scientific research, its literary version has become more or less unified and simplified with the loss of many archaic Turkic elements, bulky Iranisms and Ottomanisms, and other words, expressions, and rules that failed to gain popularity among Azerbaijani-speaking masses.
Between ca. 1900 and 1930, there were several competing approaches to the unification of the national language in Azerbaijan popularized by the literati. Despite major differences, they all aimed primarily at making it easy for semiliterate masses to read and understand literature. They all criticized the overuse of Persian, Arabic, Ottoman Turkish, and European (mainly Russian) elements in both colloquial and literary language and called for a more simple and popular style.
The Russian conquest of the South Caucasus in the 19th century split the speech community across two states; the Soviet Union promoted development of the language, but set it back considerably with two successive script changes - from Arabic alphabet to Latin to Cyrillic - while Iranian Azeris continued to use the Arabic script as they always had. Despite the wide use of Azerbaijani during the Soviet era, it became the official language of Azerbaijan only in 1978 (along with Georgian in Georgia and Armenian in Armenia). After independence, the Republic of Azerbaijan decided to switch again to the Latin script, following the Turkish model.
Republic of Azerbaijan 
Before 1929, Azerbaijani was exclusively written in the Arabic script. From 1929-1938, a Latin script was used (although it was different from the one used now). From 1938 to 1991 a version of the Cyrillic script had been used. In 1991-1992, after the dissolution of the Former USSR, a new Latin script was introduced, based on the Turkish model. However, the transition from the Cyrillic to the Latin alphabet has been very slow, and the Cyrillic alphabet is still widely used.
The Arabic script has always been used to this day.
Geographic distribution of Azerbaijani 
The estimated size of all Azeri speakers within Azerbaijan and Iran combined, according to two sources, differs from 23.4 to 30 million. This total does not include the Azeri speakers in Iraq, Afghanistan, Turkey, Georgia, Dagestan and other smaller pockets within the Middle East and Russia. Ethnologue adds 864,000 for the speakers out of Iran and Republic of Azerbaijan.
|Total population||% Azeri||Number of speakers|
|CIA Facts Book on Azerbaijan||7,911,974||90.6%||7,168,248|
|CIA Facts Book on Iran||68,017,860||24%||16,324,286|
Regions where Azerbaijani is spoken by significant group of people 
- Azerbaijani (North Dialect)1
Azerbaijan, and southern Dagestan, along the Caspian coast in the southern Caucasus Mountains. Also spoken in Armenia, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Russia, Turkmenistan, Uzbekistan.
- Azerbaijani (South Dialect) 2
East Azerbaijan and West Azerbaijan, Ardabil, Zanjan,and part of Kordestan, Hamedan, Markazi and Gilan provinces. Many in districts of Tehran. Some Azerbaijani-speaking groups are in Fars Province and other parts of Iran. Also spoken in Afghanistan, Azerbaijan, Iraq, and Turkey.
to be continued...