What the devil kind of "Nynorsk" allows "kalkuler" in place of "beregn"? And as the other poster pointed out, 'endre' does not actually take the '-leg' ending to make an adjective; not in the written language at least. Your dialect may allow it but that hardly matters. Try 'foranderlig', although I do like the idea of using articles. However, as we have three articles but variability is binary, I suggest we assign 'en' (masculine, firm, rigid) to constants, 'et' (neuter, indecisive, wibbly-wobbly) to variables, and of course 'ei' (feminine) as referring only to collections, into which things may be inserted. That does leave us with the difficulty of how to declare a collection as constant; I suggest

`ei fylke er alltid ["Vestland", "Rogaland", "Troms", "Finnmark"]`

which on second thought suggests that we can just have `alltid` as a const-modifier on `er`. Simpler.

Another point to note is that Norwegian does not allow the Oxford comma; correct grammar is "Johan, Fredrik og Martin". To follow this rule you should require the last separator of a list to be 'og':

`ei fylke er alltid ["Vestland", "Rogaland", "Troms" og "Finnmark"]`

Funny :) but I think it would work better if the language not only required Nynorsk, but used Nynorsk and not Bokmål for all keywords:

https://ordbokene.no/nob/nn/ellers

I think I also saw "ikke" in there.

And https://ordbokene.no/nob/nn/endreleg isn't a word in any language? The Nynorsk word for it is sadly just "variabel". To make it more interesting, you could require agreement, and instead of "endreleg fart", how about just using the indefinite article for things that are changeable since things that are changeable seem kind of indefinite:

    ei fart = 70
    eit smell = "bang"
    eit fag = "naturfag"
    ein slutt = "."

    forKvar fart
    forKvar slutt

    forKvart smell
    forKvart fag