The plugin comes in English, however, you can create your own translation easily. All you need is installing PoEdit, this is totally free and you can download it here
1 – Open PoEdit
Click on File – New from POT/PO file.
2 – Select PO file.
Now you have to select the PO file that comes with the plugin. You can find it in the languages folder.
3 – Select your Language.
In this example we’re going to create a Spanish translation.
You’re now ready to start with the translation line by line. Just type the translated words in the Translation box as displayed in the below screenshot.
3 – Saving your Language File.
You have to save your translation by clicking on the Save button. Please check the file’s name. The prefix has to be “bookingup-“.