Why are there tape recordings of just about everything that happened on the island? Because it was the USSR at the time, and everyone was being spied on. The only thing different about Katorga-12 is that all of the facilities were built in the 1940s, and so probably had recording devices built right into them.
Katorga-12 is the only place on Earth with this rare, time-bending element. Why? Because natural fluctuations in time around the island mutated the material of the island itself, just as E99 mutates living creatures. Alternatively, Katorga-12 is an asteroid, possible the one that wiped out the dinosaurs or caused some similarly large impact. It's the only place on Earth that you can find E99, because E99 could not form on Earth.
Okay, so having an E99-armed Soviet Union curbstomp the world in the 1960s without anyone coming up with any deterrents is implausible, right? It seems like it...until you realize that not only is the USSR's new power coming from a line of research that no one else in the 1950s has imagined, let alone done basic theoretical work in, but said research has literally given the Soviet Union time machines. If a defector steals some samples or someone at Los Alamos starts making independent discoveries, Moscow can just send someone back in time to kill them before they've done any damage. And they can do this as many times as they want.
Hey, why is the pathfinding function made out of footprints? They're yours.
The explosion at the Singularity that wrecked the island and spread E99 radiation everywhere is your fault. It's the E99 bomb you set off; You Already Changed the Past and Demichev just rebuilt the generator afterward.
Why does the description for the futuristic-looking assault rifle say it's built in the USSR? Because you changed history, and now the USSR rules the entire world in 2010!
Why do the Phase Ticks, when mutated and inflated with the TMD's de-aging function, begin to attack their own kin? Why, it's the same with humans: Reverts are universally aggressive toward all humans as well.
Here's something that will only become apparent upon multiple playthroughs: Those hidden messages scrawled in E99 dust that you reveal with the TMD? On a replay, the ones you have uncovered will remain uncovered, and any you haven't yet found will remain obscured. The messages are written by yourself from the future, who has repeatedly gone back in time to try to fix things. And you've started the game over. Congratulations, you, the player, are now complicit in creating your own time loop!
While English writings alongside Russian ones are undoubtedly a translation convention for the player, hearing Russian characters speaking in English may be not. The protagonist's last name is Renko: even if not explicitly stated, it's easy to assume he's of Russian origin and bilingual. So when he hears Russian, it's like English to him: he perfectly understands it. That would also explain why he was on a mission on Katorga, he may be sent often on Russian-speaking territories because of his fluency.
Problem being their firefight banter is still in Russian, not in English. Only their cutscene speech is in English. Maybe Renko isn't fluent enough to internally translate it under fire?
The island is called "Katorga 12." The "Katorga" was a system of penal colonies. How many of the people working on the island were actually volunteers?
There probably was a penal colony before they discovered E99. After using convicts as lab rats and to build some of the facilities and bringing volunteers renaming the island would only bring attention of spies to Katorga-12, it is easier to keep it and pretend that it is still a work camp.
It's revealed at the end that all the faded notes written on the walls were written by you. And every single one of them is true. You're pretty much stuck in a hellish cycle of death and destruction on Katorga-12 till the end of time.
Why is the Russian spoken by enemy soldiers so painfully bad at times? Because it's Soviet Union! A multilanguaged country with obligatory Russian in schools, yet not known for teaching languages well. They may be Baltic.
YMMV. The Soviet Union was a multinational state and most of its citizens throughout its history felt a sense of belonging to it. For example, at the beginning of Afghanistan War Soviet soldiers in the 40th Army were not particularly divided on nationality but viewed it as 'cool' that a comrade in arms could be from another part of the country. Balts and other nationalities were also well represented in the Party, Army, and KGB even if the high ranks of all three were dominated by Russians, Ukrainians, Belarusians and Tatars.
Singularity is a game about the kind of dread true believer Communists and/or Soviet patriots have been living since 1991. Everything they ever believed in is gone and it can be never be brought back as it was. Thus even the 'good' ending where you 'reset' to the beginning but where Barisov has become Soviet leader instead of Demichev from the standpoint of anticommunist it is still a bad ending as it means that even though it is an improvement over the initial dystopia it is still a world fundamentally at odds with your values.
Presumably the footprints you've been following around are a previous Renko's footprints who was doing what you did on a different loop. However, these footprints sometimes appear in areas where he was never able to walk (like a flooded vent that you have to swim through).
