ASCII; word "a" to "ش" I turned.

Here is how:

const char EnglishIndefiniteArticle = 'a';

static char Translate(char input)
{
    if (input == EnglishIndefiniteArticle)
       return 'ش';
    return input;
}

Please, no offense: this is how your question could be understood, really. If you think it's something else, please first see my comment to the question. Accurate formulation of the problem is critically important.

[EDIT]

By the way, if "say" means speech recognition of arbitrary text in some language, and it you hope for automatic translation of the text into another language, your problem is nearly hopeless.

—SA