Qunoot as Qunoot should be in Arabic according to the precaution, but Du'a , any Du'a (supplication) is permissible during Prayers in any language.
The Marja' of Taqleed must be the most or one of the most knowledgeable scholars in Islamic knowledge who has:
1. Full understanding of the verses of the Holy Quran with the Hadeeths related to the meaning of Quranic verses.
2. Full understanding of all the Hadeeths from the Prophet (SAWA) and his Holy Progeny (Ahlul Bayt)(AS) including the narrations of different meanings and choosing the meaning which is more authentic.
3. Full understanding of Arabic language which is the language of Quran and Hadeeths. With out full understanding of Arabic language the scholar will not be able to reach full understanding of the meanings of Quranic verses and Hadeeths.
Many non Arab scholars understand the Arabic language very well but do not speak it fluently due to no practice or little practice. This does not harm their ability to be a Marja'.
4. The ability and the practice of deriving the Islamic rules from its evidence, which is called Ejtihad. The Mujtahid is the highly learned Islamic scholar who is able to derive the Islamic rule of every matter in Shariah from its evidence in the Four Islamic sources which are: Quran, Hadeeth, Aql ( Reason) and Ejmaa'( consensus).
5. The high degree of God fearing (Taqwa) as one of the most crucial conditions of the Marja' of Taqleed as mentioned in the Hadeeth narrated from Imam Al-Askari (AS) ( Wasa'il al-Shia, Vol.18, P.131).
6. Being male born from valid marriage طيب الولادة.
The ability of giving speech in Arabic is not a condition of A Marja' as far as he has the all the above conditions.
Thank you for your question. The obligatory prayers have to be said in Arabic.
May you always be successful.
If you mean by pray, the prayers to supplicate and seek from Allah, then the answer is: Yes, it is allowed to supplicate and pray to Allah in your own language.
But if you mean by pray the Prayers (Salah or Namaz), then the answer is: NO, because Salah or Namaz must be performed in Arabic as the Prophet Muhammad (SAWA) ordered all Muslims (Pray as you saw me praying)صلوا كما رأيتموني أصلي .