I'm sure I was taught that there was at school. But someone recently asked me the difference between 'learned' and 'learnt', which is a nice little conundrum that receives plenty of attention elsewhere on SE. I tried to explain it by saying the former was the perfect past tense - as in 'I have learned', and the latter was the imperfect, 'I learnt', and that one oughtn't say (properly) 'I have learnt'. However, I began to think I was talking nonsense. I confused myself and we resorted to looking up the answer together online. It seems one is preferred in UK English and the other in American English. But in my search, I noticed that none of the pages I looked at so much as mentioned the mentioned the 'imperfect' - and I started to search for that. It's as if it does not exist. Have they stopped teaching it? Did they ever? Did they change its name? Did I imagine it?
It seems as if some style guidelines do use the -t and -ed suffixes in a way similar to the one you describe:
To muddy the waters further, a third convention requires -ed endings when the duration of the action is important, and -t endings when it is not. In other words, we use -ed endings to imply ‘action going on’ and -t endings to imply ‘action completed’
However, this is not a general rule in English, and it definitely does not constitute a separate tense. For most people, the difference between -t and -ed is purely a spelling one (with -t being somewhat preferred in BrE and -ed in AmE), and they do not carry a grammatical distinction.
In general, English doesn't have an imperfect tense the way Romance languages often do, and it doesn't have a generalized way to express an imperfective aspect the way some Slavic languages do. Instead, you'd have to rely on other constructs - for example, the distinction between "finished" and "unfinished" actions will usually be covered by the distinction between the appropriate simple and progressive tense:
I learned English. (and now I know English)
I was learning English (it was a process, and I don't necessarily know it fully now)
But sometimes, you need to rely on context:
The sunlight shone through the window. (in the context of describing a scene, probably a continuous process)
He shone a flashlight into the room. (in the context of describing events, probably a singular, non-continuous action)
The latter example would be easily distinguishable in my native Polish based on the verb's aspect (światło świeciło / on zaświecił), but in English there's no universal way to express the distinction.