To translate your Magento 2 extension, please follow the steps:
1. Open app/code/Amasty/[extension name]/i18n/ ;
2. Copy en_US.csv situated in the above folder as new.csv and rename it to the needed language code (e.g. pt_BR.csv);
3. Edit the file, replacing right side of each string with translated content:
Static content re-generation and/or cache flush are required to make that translation appear on front.