"Chan eil mi a' tuigsinn Cailean."

Translation: I am not understanding Colin.

[Annie326724]

Why is, "I cannot understand" not accepted? "I am not understanding" isn't really English!

[PatriciaJH]

It's English present progressive tense, and absolutely correct. It may not feel natural to you out of context, but it's the same construction as "I am riding a bicycle."

[ScottishDruid]

Because you are learning a different language not English. The way things are spoken that are familiar in English may not be direct translations in other languages or may not exist.

[Watson24601]

Would "I do not understand xyz" be a fitting translation? "I am not understanding xyz" just feels clunky in English

[Akhzarukhazad]

Because "I am not understanding" is a more direct translation, so that it's easier to understand what's going on.