I had to deal with this, except for it was Spanish & Portuguese and not Russian. My store was in a complex where the building had outside security. They did not allow their employees to speak Spanish/Portuguese on the job. They let us know that our employees were not allowed to speak to their employees in that language, either, and it was vetted by lawyers from our company.

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We also had to ban all foreign language use by our employees after two young men were overheard from the breakroom having an apparently extremely graphic and inappropriate conversation by a patron. They were speaking a somewhat obscure variant of Cantonese. One of the biggest issues was that they claimed they said something that was in poor taste but kinda funny play on words and the patron claimed it was something highly inappropriate, racist and sexist. It really depended on who translated it. And in the end, it really didn't matter. We banned all employee conversations in foreign languages because even if we could monitor them there were too many nuances in translation.