Disclosed are systems and methods for execution of program code by an interpreter. One exemplary method comprises: generating intermediate instructions based on a unified grammar from instructions of the program code, beginning execution of the intermediate instructions in an emulated computer environment, in response to detecting an instruction of the program code associated with an object for which a rule of interpretation is not found, halting further execution of the intermediate instructions, obtaining an auxiliary code corresponding to the object, wherein a result of execution of the auxiliary code corresponds to the result of the execution of the object, and wherein the auxiliary code contains objects for which the interpreter has a rule of interpretation, executing the instructions of the auxiliary code; and after completion of the execution of the auxiliary code, resuming the execution of the intermediate instructions.