a -> i -> u -> a
e <-> o
k -> t -> p -> k
g -> d -> b -> g
To make the process easy, start by inserting a delimiter character, such as @, before every instance of one letter. For instance, replace 'a' with '@a'. Then change 'u' to 'a', then 'i' to 'u', and finally '@a' to 'i'. Repeat the process for the other strings of replacements. You can either leave "match case" turned off, and put up with a few oddly uncapitalized words in the final text, or have it turned on and do the whole process again for the capital letters. (Personally I'd consider that too much work. But maybe someone other than me will program an automatic text filter!)
The results are bizarre! It looks like some wacky foreign language, or some incomprehensible dialect of English.
Here's an example, made using one of my own recent LJ posts:
"Pho oxhiasp fin un pho gict giphreem
...greto bewn i fow menphs ide. Bib oximunob up inb fudarob up noobob roklicund, gap un pho krecoss ef romevund up frem pho coulund, ho bocubob pe pry duvund up i gup ef i cloinund. Ifpor vicaamund ill pho basp & crab eap ef up, ho feanb up wealb parn idiun! Kappund up gict pedophor wis pho hirb kirp. Up unvelvob gelpund sovoril kuocos pedophor, phon socarund pho gelps wuph peephob naps phip hib egvueasly goon kap en un pho ficpery gofero pho fin wis ippichob, gap wo cealbn'p romevo pho fin wupheap bospreyund pho lupplo beehuctoy helbund up en. Se U pruob... inb ovonpailly dep pho naps un klico, phints pe semo imizund minail boxporupy! Phon Bib kap pho issomgly gict un klico, inb up wertob idiun!
Lipor un pho biy, Mem inb U wonp eap pe kuct ak semo skidhoppu frem eluvo dirbon. U ilse dep mysolf i checelipo lisidni, whuch U jasp funushob. Yam!"
Why not try playing around with other combinations of letter swaps to make? See what sort of bizarreness spills out!