بسم الله الرحمن الرحیم
الحمدلله خلق الانسان علَّمه البیان نَزَّل القرآن بلسان عربیّ مبین، و الصلاة و السلام علی النبیّ العربیّ سیّد ولد آدم و خاتم الانبیاء و المرسلین
As far as I searched, there is no tradition to point that it is deemed as a Wajib (mandatory) practice for Muslim, but there are some case which make us learning Arabic. For example by learning Arabic, perhaps we can comprehend the holy Quran better which is in Arabic language, or in reading the origin hadiths and so forth.
On the other hand, Arabic language is considered as one of the most populous languages and in accordance with my research, Arabic is counted as the Sixth language of the world (from the aspect of the population).
There is a hadith from Imam Ali (peace be upon him) that says:
« تَعـَلـَّموا العَرَبیّــﮥ و عَـلِّـموها النّاسَ . Learn Arabic and
teach it to the people.
Or Imam Sadiq (a.s.) said:
تَـعَـلَّـموا العَرَبیّــﮥَ فَـإنَّـها کلامُ اللهِ الَّـذی
یُـکَـلِّـمُ بِـهِ خَـلْـقَـهُ .
Learn Arabic, because this is the speech of the God who speaks to his
creatures.
Even Imam Khomeini has illustrate concerning the significance of
learning Arabic:
Do not say that Arabic is not from us, Arabic language is from us,
Arabic language is the language of Islam and Islam is for all people.
It can be investigated from other aspects like:
Being able to speak with Arab Muslims in interchanging the Islamic knowledge and civilizations and so forth.
Being able to have discussion with other Muslims (Arabs) regarding Islamic issues such as Quran, hadiths and so forth.
Being able to watching other Islamic Arabic channels of TV and radio and obtaining Islamic and scientific revenue by watching and
hearing them.
Finally it could be a more unity between Muslims in different languages.
Reference(s):