IronBar: English version has limited voice acting, mostly for unique and important dialogue. Clear Sky and Call of Pripyat had some more English voice acting such as greetings and "put your gun down" lines.

Most idle, combat and other dialogue are still in Russian.

The English voice acting isn't Resident Evil 1 level or anything. Most of it's pretty good. Some lines might be a bit silly but that's about it.

You might also be able to find mods that replace all dialogue with Russian.

Shouldn't be a problem unless you want absolute 100% immersion.

Concerning subs, the games don't have subtitles. Only text in dialogue boxes and radio communication (which also doesn't match the dialogue in SoC most of the time.)

MrLongPants: Seems like kind of a half assed localization.

F4LL0UT: I'm among those people who actually loved the localization and I think it contributes to the atmosphere - I wouldn't call it "half assed". Some people don't appreciate the concept of the localization but to each their own, I guess. They kept as much of the original Russian (or Ukrainian, I really don't know the difference) language and inserted English voice acting wherever it seemed necessary for the player to actually understand the phrases, with an accent, though, so it kinda fits in with the predominantly Russian voices and without a need for subtitles outside of dialogue screens.

F4LL0UT: I'm among those people who actually loved the localization and I think it contributes to the atmosphere - I wouldn't call it "half assed". Some people don't appreciate the concept of the localization but to each their own, I guess. They kept as much of the original Russian (or Ukrainian, I really don't know the difference) language and inserted English voice acting wherever it seemed necessary for the player to actually understand the phrases, with an accent, though, so it kinda fits in with the predominantly Russian voices and without a need for subtitles outside of dialogue screens.

1322: ^This. I quite like how they've done it. I don't think the English hurts the game at all. Still plenty of Russian/Ukrainian banter around that keeps the immersion factor quite high.