Abu ʿAbdillah Muhammad ibn Idris ash-Shafi’ee 204 AH [May Allah have mercy on him] said,

أن اللسان الذي اختاره الله لسان العرب فأنزل به كتابه العزيز, و جعله لسان خاتم أنبيائه محمد صلى الله عليه و سلم و لهذا نقول: ينبغي لكل أحد يقدر على تعلم العربية: أن يتعلمها, لأنه اللسان الأولى بأن يكون مرغوبا فيه 

“The language that Allah favored/chose was Arabic. He revealed His glorious Book [The Qur’an] in this language and He made it to be the language of His final and last prophet, Muhammad -peace and blessings be upon him.  Therefore, we say: everyone who has the ability to learn this language should do so, because it is the most desired language [one should learn due to the Qur’an and the Sunnah being revealed in it].” 

Source: Sharh Iqtidaa as-Siraat al-Mustaqeem pg. 342 [Official print from the Mu’assasah ash-Shaykh Muhammad bin Saalih al-‘Uthaymeen al-Khayriyyah]