That's definitely a bit odd, as I'm seeing the messages as intended in Chrome, with UTF-8 set as my encoding. Are you able to try from a different computer, and replicate that same behavior? If so, could you provide us with the confirmed encoding, the browser, and the browser version?
To answer your question, these translations would reside in both the .mo and .po files in the /po/ directory of your plugin installation. The content of which can be checked by opening it in either a regular code/text editor, or by using software like POedit.
We look forward to hearing back!