Comment by samsaga2

If the languages are similar:

  1. Tokenize
  2. Build AST tree
  3. Emit target code from the AST tree

If they are very different:

  1. Tokenize
  2. Build AST tree
  3. Create a simple intermediate language from the AST tree
  4. Emit target code from the intermediate language

It is the same as building a whole compiler, but without the optimization/register allocator passes.