How can i translate the weahter API content from EN to SP ?

I look up for the response to use the Celsius Degrees in the app response

´´´ swift

let baseURL = NSURL(string:"https://api.forecast.io/forecast/\(apiKey)/")

let forecasrURL = NSURL(string:"19.429418,-99.205582?units=si", relativeToURL: baseURL)

´´´

Reading the API documentation it refers that we can use some other languages:

lang=[language]: Return text summaries in the desired language. (Please be advised that units in the summary will be set according to the units option, above, so be sure to set both options as needed.) [language] may be bs (Bosnian), de (German), en (English, which is the default), es (Spanish), fr (French), it (Italian), nl (Dutch), pl (Polish), pt (Portuguese), tet (Tetum), or x-pig-latin (Igpay Atinlay). (If a different language is desired, please consider contributing to our API translation module on Github.)

But where do i declare the other language that i need to display within the code?

Any help?

Thanks.