السلام عليكم ورحمة الله وبركاته
One brother has stated that Urdu is "the second language of Islaam". I would just like to make a small correction:
Urdu is one language from the languages of the Muslims. Islaam, on the other hand, has only one language, and that is Arabic. Arabic is the language of the Qur'aan, the language of Jannah, the language of the Malaa'ikah, the language in the Qabr, the language of Rasoolullaah صلى الله عليه وسلم and the language Allaah Ta`aalaa has chosen for this Ummah.
`Allaamah ibn `Asaakir رحمة الله عليه narrates in "at-Taareekh" that the language Nabi Aadam عليه السلام spoke in Jannah was Arabic.
Imaam Abu Bakr ibn Abi Shaybah رحمة الله عليه narrates that Ameer-ul-Mu'mineen Hadhrat `Umar رضي الله عنه said:
تعلموا العربية فإنها من دينكم
"Learn Arabic, for it is part of your Deen."
In fact, Hadhrat `Umar رضي الله عنه did not want those who are fluent in Arabic to speak any other language. He said:
لا تعلموا رطانة الأعاجم
"Don't learn the languages of the non-Arabs."
This was addressed to those who were fluent in Arabic.
It must be stated here that, for those who are not fluent in Arabic, there is no harm in speaking other languages, whether it be Urdu, Gujirathi, English, etc. amongst one another. However, two people who are both fluent in Arabic should not speak any other language with each other besides Arabic.
Imaam ibn Abi Shaybah narrates that once, Hadhrat Muhammad ibn Sa`d ibn Abi Waqqaas saw some Muslims speaking in Faarsi (Persian), so he asked them, "What is the matter with you that you have chosen Majoosiyyah (fire-worship) after having had Hanafiyyah (Monotheism)?"
That was how opposed he was to people capable of speaking Arabic fluently, choosing to speak in other languages instead.
In summary:
Islaam has only one language, and that is Arabic. All other languages are permissible, but they are not "Islaamic languages". They are languages spoken by Muslims.
والله تعالى أعلم
(P.S. I can read, write, speak and understand Urdu, but I rarely ever do so.)
والسلام