The document discusses language translation using lex and yacc tools. It begins with an introduction to compilers and interpreters. It then provides details on the phases of a compiler including lexical analysis, syntax analysis, semantic analysis, code generation, and optimization. The document also provides an overview of the lex and yacc specifications including their basic structure and how they are used together. Lex is used for lexical analysis by generating a lexical analyzer from regular expressions. Yacc is used for syntax analysis by generating a parser from a context-free grammar. These two tools work together where lex recognizes tokens that are passed to the yacc generated parser.