Download Pedit from https://poedit.net/

Run installer and proceed with installation

Start Poedit and select "Open" from top menu

Select .po file to edit, probably located in <project folder> → website → locale → <locale name (Language COde) > → LC_MESSAGES and click "Open" in the right bottom corner

Now you can see list of texts to translate on the left

Select from text from the list you want to translate and put translation into box at the bottom

After you added some translations you need to check them for any errors, select “Validate” from top menu

At the end you can save your work by selecting "Save" from top menu