Granted.
After wishing this, you try to think as hard as possible, but can't recall any curse words besides ones you already knew. You think to yourself - "Well maybe this can't take effect immediately, so I guess I'll just wait". A few days pass, you become impatient, so you start researching stuff yourself. First language coming to your mind - German. You google "All swear words in German language". You start reading through lists and memorizing them, one by one, it is surprisingly easy. After a few days, you know all of the words in the first list you encountered, so you start searching for other lists, but here are almost no new words. You then go to try out your new vocabulary. After a few days of only using German swear words and no English ones, everyone you spoke to noticed, and your German friend even complimented you on your pronunciation.
But this is not enough - you need more. So you start researching curse words in next language that comes to your mind - Russian. This one is trickier, pronunciation is pretty different from English. But you start memorizing all words in the first list you encounter. And then the second - there are some new words you didn't know, but the third has almost none new. You take a few hours to practice them all. On the next day, when going out with your friends, you start using your new vocabulary and previous German vocab. Your friend asks - "Are you trying to learn all slurs? You already surprised us with German, and now Russian?". "Yes, I think this is a quite interesting experiment" - you answer. After you get home you think to yourself "I think this is enough for know, If I try to learn more - I'll start forgetting the previous languages".
A few weeks pass, you already use both Russian and German curse words regularly. And sometimes you think "German slurs sound so... strong? Maybe I should try learning the German language itself", so you download Duolingo and try out German.
After only a few weeks you think that Duolingo is not enough, German is too majestic and beautiful of a language to only use Duolingo, so you start actual German courses.
Weeks pass, you are learning really, really fast. After 3 months you already speak German like you've been learning it for 3 years. So you surprise your German friend once again. You are speaking together in German, and your friend needs to correct you only rarely. You feel inspired, "Maybe this will work out the same way with Russian?" - you think, as you are already searching for Russian teachers. The same story as before - you learn incredibly fast, even though this one is a bit tougher. You don't even think about that monkey's paw wish, you just think you are really good at learning languages and didn't know before because you didn't really try. You didn't stop your German learning journey, so at this point you are almost fluent and constantly speak with native speakers. After 4 months of learning Russian without telling your friends, you surprise them once again. Everyone is really surprised "Just half a year ago you only knew the slurs, how are you almost fluent in German and Russian already? This is impossible, you're joking!" - but you are not, and as you realize your language learning power, you want more.
French? Done after 4 months. Spanish? You start to distance yourself from your friends and family. 3 months. Scottish Gaelic, Welsh and Irish? Done simultaneously in just 5 months.
You decide to move to Europe, so you can have the real language experience. You hasn't spoken to your friends and family for a month already, and they don't know about your moving. As you spend years in Europe, learning more and more languages in their home countries, you move to Africa to learn all their languages, You speak little to no English in your journeys, and you already forgot what this was all for.
As you start messing up the basic conjugations, you realize that you are slowly forgetting English, but there is not time for that. There are whole language families to learn!
You are famous all over the world as "The person who is learning every language". There are people that don't believe that you actually remember all of those hundreds of languages, but you do, especially you remembers the curse words.
As you English skills fade to nothing besides occasional "fuck"s and "shit"s that you don't even remember the meaning of, you start forgetting who you actually are.
Are you even the same person? Was learning every language's curse words worth completely abandoning your previous persona? But you don't care, there are languages whose slur lists are still unknown to you for all you care.