"Anakku demam tinggi."

Translation: My child has a high fever.

[StephenL1]

Native English speaker here. I've never used the phrase "high fever". A fever implies high temperature so "high fever" is redundant.

[KyrieDomineJesus]

Whut...? Naw... I'm not native, but I am very certain that "high fever" is a thing - at least in some parts of the English speaking world. I'm quite sure I remember reading that expression before.

You can have a normal, moderate fever. That's somewhere between 38 and 39°C. Then if you go 40 or seriously beyond: that's a high fever!

[janis.w]

Same, as a native speaker I would just say "he has a temperature" - I have never used or heard the phrase "high fever"