Como os pilotos “agressores” poderiam pilotar aeronaves estrangeiras sem falar o idioma?

A couple of things come to mind that enable this:

• you don't become a fighter pilot if you are not intelligent and highly motivated
• you are not learning a new skill, just doing what you are already trained to do in an environment that just looks different (this would somewhat exclude Russian helicopters)
• the list of things to learn is really not that long, I'm taking the liberty to throw in a guess of 100 items
• you have a huge organization backing you up (translations as mentioned in comments, intelligence data etc.)

So: You are a person that is able to fly fighter jets, most probably you are damn good at it if you are given the opportunity to fly a fighter caught from the enemy.

You learn new stuff easily, and you are thrilled to do this, which of course helps in the learning process. Your organization provides you with pretty much every bit of information about the task you are about to undertake, translated manuals etc.

Regarding the cockpit language barrier, it's not that hard to learn the labels on switches and gauges. For example the picture in the question: I took a not-so-wild guess that it's an altimeter, checked with translator and yes: высота is altitude in English (pronounced something like vysota but that really doesn't matter). From now on, when I see text that says высота, I know it means altitude. On Russian planes the pilot just has to remember the altitude is in meters, but since the label looks "weird" I don't think there's much chance of a mix-up.

Anyways, when operating a fighter jet, you learn the location and operation of the critical switches and systems by heart, you não browse around the cockpit searching for switches when you need to do something.

Once you've become familiar with the user interface, the basic flying will be pretty much the same as in any western fighter.

P.S. There's one thing that really helps: Cyrillic numbers are not used anymore :)

You don't need to speak(1) fluent(2) Russian(3):

1. In fact you don't need to speak absolutamente, just understand.
2. You don't need to be fluent, just understand enough to not crash the plane.
3. It's not about Russian, it is about Russian Aviation Jargon. (Think about English: if you walked up to a random person on the street and started talking about laminar flow, elevons, flaperons, flat spins, etc., then from their perspective, you might just as well speak Russian!) We are talking about a couple of dozen terms at most, and highly standardized technical terms at that. Also, physics and aerodynamics work the same everywhere, so there are going to be a lot less cultural differences and a lot more straightforward 1:1 translation.

Last, but certainly not least: we are talking about trained and experienced test pilots. It is literalmente their job to fly airplanes they don't know how they will behave, and figure it out as they go along.

Just to add: I was at an airshow in Australia once in the 90's and the radio announcer said the MiG-15 which was flying had labels on all the instruments to meet the CASA (Civil Australian Safety Authority) regulations to be allowed to be registered here. Sure enough, all the instruments had sticky-back DYMO labels (the old style, with the white stamped/embossed lettering on the coloured plastic strips). This is just what I remember him saying: I wouldn't vouch for it being part of the regulations as that's getting off-topic.

I can't guarantee it's the same aircraft I remember seeing, but this is exactly what I mean:

Addition: In the cold war era, quite a lot of documentation for Russian equipment seems to have been available (well, existent) in German too (eg you can find training films for setting up antiaircraft batteries on youtube, in German), plus some export versions of Russian-made gear with German labelling. The reason is that the Nationale Volksarmee in East Germany was supplied with various Russian equipment, and obviously needed to be able to operate it.

This extends the circle of people who can help - also, there were friendly ties with the West German Bundeswehr (who did not use Russian equipment but could certainly help with anything labelled in German).

Não é aquele hard to learn a language, certainly the technical parts. However it's a bit more than words; for instance Soviet attitude indicators work very differently.

You just need to think in Russian :)

As a non-native speaker for both English and Russian I can confirm that you don't really have to speak (or even read) some language in order to operate a more or less familiar machine labeled in that language.

Most people from smaller nations are used to this, those that were young in 1953 - even more so.

In this part of his TED talk, Col. Chris Hadfield recounts his return from the ISS in the Soyuz spacecraft.

His speech is about how the experience could have been scary and overwhelming, but

"instead, twenty years previously, we had started studying Russian. And then once you learn Russian then we learned orbital mechanics in Russian, and then we learned vehicle control theory, and then we got into the simulator and practiced over and over and over again"

This is a slightly different situation since it was a collaboration between Russia and NASA, but it goes to show that pilots can learn to fly pretty much anything with instruments labelled in any language.

That would not be required as an experienced pilot can find their way around the cockpit with relative ease. You can spot the basic flight instruments, navigation instruments and engine instruments with ease. Additional systems can be re-placarded as well by native language speakers. In addition most of these ‘acquisitions’ were turned over by defecting pilots who are generally happy to brief our test pilots on the system functions in question prior to flight. If you were a test pilot selected to be part of constant peg or similar reverse engineer program, you would receive quite a lot of briefings from the intelligence community and technicians who have worked on that aircraft prior to ever getting in and flying it. You will be fairly well-versed in the systems and their operation prior to your first flight.

I'm not a pilot or aviation expert but I think one point is missing. I think the majority of aircraft are designed to operate on ground without actually flying. That's because to make pre checks. It would be easily fatal if you need to check a critical system mid air to find out it's failing. Thus you can try out all basic systems to fly on ground in safety and without time pressure. After you figured that out you can at least fly by manual systems. Which likely most aircraft have as well as backup. Don't you think?

It is not the gauges that are the problem.

Think of it as something you might be more familiar with, like a car from the 1950's

As long as you are traveling during the day and paying attention to the vehicle, they gauges don't really tell you anything you can't estimate on your own. They just give a bit more detail.

It is the switches that are difficult. Have you ever driven an unfamiliar car, and accidently turned on the windshield wipers? Same thing here. You need to know what switches do what, you can figure that out when your not moving, and re-label or memorize.