Haukur wrote:

<This is correct:
<He insisteth that she go.

<But this isn't:
<*He insists that she goeth.

The examples here are not dirct equivalents in English of the Norse
change in endings. The older English ending <-(e)th> is 3rd per.
Present indicative not subjunctive, whereas Norse <fari> is present
subjunctive, isn't it?

You can say in English:

"He insists that she go" (subjunctive)
"He insists that she goes" (indicative)

Both equally right and quite common.

Dan