Because when the Buddha went to different countries, he would use the languages of different countries (the countries of India at that time), and most of them used Pali.

Because it is very simple, the Buddha taught liberation in order to liberate the audience-now Buddhism is regarded as Buddhism, in fact, Buddhism is not a religion, but an education, and all teaching requires practice-so only the language that the audience can understand is used.

Only by giving lectures can we get rid of the audience.

Secondly, every country has its own monks who translate Buddhist scriptures, so it is natural for Buddhist scriptures to be translated into various languages. Chinese characters are only one version, and there are German, English and Thai.