this is recited in Arabic first and then in the persons own language. We say:
“Ash-hadu an La Ilaha Illallahu, wa Ash-hadu anna Muhammadur RasulAllah.”
“I bear witness that there is no God but Allah, and I bear witness that Muhammad is the Messenger of Allah.”
This lets people know that you are a Muslim and that you acknowledge that it is Allah who is the One who has given you life and all the blessings in your life.
“He who obeys the messengers obeys Allah.” [An-Nisaa 4:80]
Allah sent prophets in different periods of time to communicate His guidance with human beings. They were raised from the nation in which they were sent to preach for. They preached in the languages of there nations as the Qur’an says:
“And We never sent a messenger save with the language of his folk that he might make (the message) clear for them.” [Ibrahim 14:4]
“And there not a nation but a warner has passed among them.” [Fatir 35:24]