Russian conditional sentences work slightly differently compared to English:
Things that actually happen: E: If [something in the present], I [something in the present]
If I drink coffee at night, I don’t sleep well. R: Если я пью кофе на ночь, я плохо сплю. (If + Present Imperfective, Present Imperfective) Option: Если я выпью кофе на ночь, я буду плохо спать (If + Future Perfective, Future Imperfective).
These two options (with present and with future) are completely interchangeable.
Things that will happen in the future if conditions apply: E: If I drink coffee tonight, I won’t sleep well.
In English, the if-part is in the Present. In Russian, both parts are in the Future: R: Если я выпью на ночь кофе, я не засну / я буду плохо спать.
The if-part is perfective here, but it works for both type-1 and type-2 sentences. Russian doesn’t differentiate here unlike English.
Imaginary/ unreal situations in the present or future: E: If I drank coffee tonight I wouldn’t sleep well. R: Если бы я выпил (выпила) кофе на ночь, я бы плохо спал (спала). Note: Both parts of the Russian conditional sentence is in the Past and contain бы (=would).
Imaginary or unreal situation in the Past: E: If I had drunk coffee last night, I wouldn’t have slept well. R: Если бы я вчера вечером выпил кофе, я бы плохо спал.
Technically, type 3 and type 4 are the same, only “last night” - вчера вечером - indicate the Past.
I’m afraid I should choose between Icelandic and Swedish, and between Russian and German, for the next few years. I can’t keep all of them at the same time, even though I’d really love to. It’s all so sad.