Shaykh ʿUbayd Al-Jābirī was asked:

May Allāh preserve you, this questioner says in in his question: Have any evidences established that the people of Paradise will speak in the Arabic language?

He answered

Until now, I do not know of any evidence for that, however they will speak and that which is apparent to me is that they will understand the each other’s speech.

Source: Miraath.Net
Translated by Abū ʿIyāḍ @abuiyaadsp

السؤال : حفظكم الله هذا سائل يقول في سؤاله: هل ثبتَ بالأدلة أنَّ أهل الجنة يتكلَّمون باللغة العربية؟ الجواب : حتى الساعة لا أعلم دليلًا على ذلك، لكنهم يتكلمون، والذي يظهر لي أنَّهم يفهمونَ كلامَ بعضهم. نعم