How about calling them a "clear glaze" and a "red glaze"?

"Tortenguss" as such is not available here - at least in UK. So I'd use "gelatin glaze" made from powdered gelatin or leaf gelatin/gelatin sheets, since glaze alone could also be warmed sieved jam. For red Tortenguss I think you would have to colour that with food colouring; AFAIK there is no red leaf gelatin available here.

Not necessarily gelatin - why not arrowroot? ;-)
And I think Dr. Oetker Tortenguss is available from some outlets in the UK ...

Have to admit that I have never tried arrowroot - is that neutral in taste?
You could get Dr Oetker Tortenguss from online shops like Germen Deli, but I meant it's not widely available in the shops here.
Hi Marianne!

Isn't it possible to use cornflour or Gelierzucker to make a non-gelatine Tortenguss?

I've never used arrowroot, but the cooking shows of my youth always recommended it as neutral taste. In theory, corn starch would work.

Thank you for all the replies!

In German, if you say "Tortenguss," there is usually just one specific type of product (not a brand) associated with it: a powder that is stirred into boiling water, sets, and then solidifies once it cools down.

I was hoping there was one word describing an equivalent product that you would go out to buy, preferably one that both British and US speakers would understand.

It does not really matter what exaclty it is made of, rather that the result is the same/similar to that of the German Tortenguss.

I don't think you'll find a specific word for it -- at least for AE, that type of cake/tarte is rather rare. #1 is about the best you will get, but won't much to many people unless they are familiar with the concept or have a broader experience of cooking.