In portal 2, you have the option to choose what language you want for the game, this will affect the audio and subtitles, however, in portal 2's files, there is an option for "pirate" listed in Steam\steamapps\common\Portal 2\portal2_dlc2\resource


I have no idea why this was made or why it was cut

In the launch options when you right click on portal 2 and properties, you want to type in " -language pirate "

Now that you have typed that in the launch options, just launch the game and it should display the pirate language

I'm pretty sure most of the game is still in English, i think that some lined are translated to pirate, you can look in the game files for all of the dialogue that this effects

So, now that you have enabled pirate language, uhhhhh...
I don't know what else you want to do with it, it's just something to mess around with