14:4
وَمَا أَرْسَلْنَا مِن رَّسُولٍ إِلاَّ بِلِسَانِ قَوْمِهِ لِيُبَيِّنَ لَهُمْ فَيُضِلُّ اللّهُ مَن يَشَاءُ وَيَهْدِي مَن يَشَاءُ وَهُوَ الْعَزِيزُ الْحَكِيمُ
We sent not a messenger except (to teach) in the language of his (own) people, in order to make (things) clear to them. Now Allah leaves straying those whom He pleases and guides whom He pleases: and He is Exalted in power, full of Wisdom.
16:103
وَلَقَدْ نَعْلَمُ أَنَّهُمْ يَقُولُونَ إِنَّمَا يُعَلِّمُهُ بَشَرٌ لِّسَانُ الَّذِي يُلْحِدُونَ إِلَيْهِ أَعْجَمِيٌّ وَهَـذَا لِسَانٌ عَرَبِيٌّ مُّبِينٌ
We know indeed that they say, "It is a man that teaches him." The tongue of him they wickedly point to is notably foreign, while this is Arabic, pure and clear.
30:22
وَمِنْ آيَاتِهِ خَلْقُ السَّمَاوَاتِ وَالْأَرْضِ وَاخْتِلَافُ أَلْسِنَتِكُمْ وَأَلْوَانِكُمْ إِنَّ فِي ذَلِكَ لَآيَاتٍ لِّلْعَالِمِينَ
And among His Signs is the creation of the heavens and the earth, and the variations in your languages and your colours: verily in that are Signs for those who know.
41:4
بَشِيراً وَنَذِيراً فَأَعْرَضَ أَكْثَرُهُمْ فَهُمْ لَا يَسْمَعُونَ
Giving good news and admonition: yet most of them turn away, and so they hear not.