You can set up the different default languages for your editable elements (instances) on the same page using the init() WProofreader initialization by using the lang and syncOptions parameters:
1) Initialize WProofreader using the init() method when you clearly know in which control you want to initialize WProofreader that provides additional management options.
2) Pass the language using the lang parameter and the appropriate shortcode in WEBSPELLCHECKER.init.
3) Disable synchronizing synchronizing ignore options and languages between all the created WProofreader instances using the syncOptions in WEBSPELLCHECKER_CONFIG.
syncOptions: false,
4) Also, it would be check and if needed to disable storing of WEBSPELLCHECKER options such as language between browser sessions using disableOptionsStorage in WEBSPELLCHECKER_CONFIG.
disableOptionsStorage: [lang],
