Currently Spark is automatically setting the language of the current regional settings of Windows no matter what other language besides English you select. E.g. if your regional settings are English and you select Portuguese language, then it will switch to English. If your reg.settings are Russian and you want to switch to Portuguese, it will switch to Russian. Though it work fine if you select English language and switches to English.
Correction. This is only happening with the double named language files like spark_i18n_pt_BR.properties. If you rename this file to spark_i18n_pt.properties and save spark.jar when you'll be able to select Portuguese language with not Portuguese regional settings.