There are no rules, but a few tendencies:
Older and frequently used loanwords are more likely to be adapted to the Norwegian writing/sound system. The same goes for loanwords whose original spelling differs greatly from how a Norwegian would transcribe it.
Many French and Latin loanwords came into the language via the nobility, and the words that were decidedly upper class or highbrow of nature are more likely to have retained their original spelling. Their true French/Latin form would have been considered more refined by the upper class, and since those of more meager means had little use for the words to begin with they also had no incentive to change the spelling.
The French accents are retained in cases where they mark a syllable which usually wouldn't be stressed in Norwegian. Norwegian generally pronounces the letters that would be silent or near silent without the accent in French, so this is solely about stress.
In most languages, they either use something like "take" or they use a specific verb for showering. English is quite an outlier with its having of meals, showers, good times, etc.
It is an important part of English, however, and "have" should be the primary translation here, rather than being marked as wrong as it is now. I'll go and report it now.
I disagree that have should be the primary translation, at least in American English. I don't have showers, I take them.