The Russian translation for "effectiveness" seems to be "эффективность", a word that sounds pretty similar to "effectiveness" and also initially would seem to be able to be used interchangeably to describe the same concept in both languages.
However, the Russian translation for "efficiency" is also "эффективность".
"Effectiveness" is about the capability of producing a desired result, or how close something/someone is to achieving a desired result (or sometimes also how much of the desired result it achieves).
"Efficiency" on the other hand is about the ratio of the desired outcome compared to the resources it took to achieve. The amount of productivity vs. the amount of waste.
These two words are used to describe distinct concepts in English, but these concepts are seemingly merged into one word in Russian.
I'll give a particularly absurd example of how this can lead to confusion to help illustrate my point:
If I were a manager and I noticed that a Russian worker I was supervising had an output that was of high quality, met all of the client's requirements, and never had any mistakes, then at their performance review, I would want to tell them "You're very effective at performing your job." In Russian, it seems that saying "Вы очень эффективно выполняете свою работу" to them would be a reasonable way of going about that.
If that Russian worker was also slow, though, sometimes not able to meet deadlines because they were obsessing over the details to achieve such good output, I might then also say, "Though you're not particularly efficient at performing your job", which, if I also wanted to tell them in Russian, I would say "Хотя вы не особенно эффективно выполняете свою работу".
I haven't looked into the etymology, so I'm not speaking from a place of knowledge. If I were to take a guess though, based purely on how they sound, the word "эффективность" seems to be derived from the word "effectiveness" (or they share a common ancestor). Somewhere along the language's evolution though, Russian also added the concept of efficiency to that word, instead of as its own separate word.
This seems to also be true when the words are used in more technical contexts with things like "energy efficiency" translating to "энергоэффективность".
In a technical setting, if you wanted to avoid any ambiguity, it seems like the simplest way to talk about efficiency in Russian would be to say "коэффициент полезного действия", which is a mouthful but gets the point across.
For a non-technical and especially for a casual context though, I haven't been able to find any satisfactory and straightforward way (a way that is both effective and efficient, if you will 😉) to express the concept of efficiency in Russian without having it mixed up with effectiveness, or vice versa.