Start using satan as an expletive and just claim you're Scandinavian. If you fancy with it use "fanden" (you can pronounce it like "vain" with an "f" instead of a "v" and claim you have a copenhagener dialect).
To really sell it say "for" beforehand. "Av for fanden!" = "Ouch for satan" (fuck that hurt).
Fanden tage det = Devil take it (fuck it)
Fandens også = Devils' too (damn it didn't go well)
In these instances I'd recommend not taking the whole phrase, but just substituting the expletive with fanden. This worked very well when I went to school abroad.
So you'd be saying things like "fanden it" and "Ouch! Fanden! Fu-Fandens too!"

Another good one is "sgu" which functions as chinga or fuck - as in "i don't wanna fucking do that" you can say sgu instead.

Røv = ass and is great to yell. Get real guttural with the r. Here is some inspiration
Lort = shit and is also great to yell. Pronounced like lohrt or low-rt (trying to get you to figure out the vowel sounds here).

Spurgt? = Asked? As in "who asked you?" Or just the verbal equivalent of sending a thumbs up emoji to a long text. Pronounce it like spoo-art, but quick.

Fanden i helvede = the Devil in hell, great for when you stub your toe. Good luck with the pronunciation, the trick is to ignore the letters. You can basically just say "fain ee hell" and be understood.

Jeg elsker dig = Its like a curse, you just generally curse a person or a situation. Great allrounder.

Jävla is Swedish, so I wouldn't bother but if you must it's a good suffix to words. Swedes say danskjävla for example which means danish devils. The Danes do not have a similar word for swedes, because being swedish is bad enough.

Fjeldabe = Rocky plateau monkey (not racist its about white people) you can use it for people who have a ski hut in Aspen.

Så er den ged barberet! = That's that goat shaven then! (That's that task done)

Kammerat = Comrade/buddy

I'd give you some Spanish, but sounds like you've got enough.

mainly just dirty curse phrases

Satan i hælvette ka slags fetteforbanna mannskitt e dette?

Basically just means "what the fuck is this?" but with more swearing.

You can end sentences with "lan" as an exclamation mark and instantly make it (more) aggressive! Works especially well on questions. But makes non-questions extra spicy.

E.g. ranked least aggressive to most:
"I don't know" < "How should I know?" < "How should I know lan?" < "I don't know lan!"

Other examples:

• Stop getting on my nerves lan!
• What's this lan?
• What are you doing lan?
• Fuck lan!

Or start of the sentence can work too e.g. both of these differ only in where the emphasis is:

• Lan, why is the trash still here, didn't I just tell you to take it out? (You're more enraged about the trash still being there than the other person not listening)
• Why is the trash still here, didn't I just tell you to take it out lan? (You're more enraged about them not listening than the trash)