While the software is natively in English, the "RUS" suffix in searches usually points to two things:
The phrase (Russian for "download Proteus 8 for free in Russian") is a common search term used by engineers, students, and hobbyists looking for a localized version of one of the world's most powerful electronics design suites. What is Proteus 8?
Unlike many free alternatives, Proteus can simulate the interaction between software running on a microcontroller (like Arduino, PIC, or STM32) and the analog/digital electronics connected to it.