According to Esctoday.com , the Spanish national broadcaster has confirmed that Barei will sing her song completely in English in Stockholm.

It means that Spain will participate with a song which is entirely in English for the first time. Until 2008, Spanish artists performed on the Eurovision stage with native language. Rodolfo Chikilicuatre who represented Spain in Belgrade prepared his entry by using Spanish & English for the first time in history. Also Soraya and Ruth Lorenzo had chosen this way!

http://https://www.youtube.com/watch?v=X-lHEiff5ZQ
As you know, Spain has determined its participant with a national final, and Barei is gonna perform “Say Yay” on the stage. The lyrics of this song is combined with English and Spanish. But the final version will be entirely in English.

https://www.youtube.com/watch?v=SNOzBoE3H0I