For the translation, you can find the language constants here: /language/en-GB/en-GB.com_jamegafilter.ini
For example:
COM_JAMEGAFILTER_SORT_BY="Sort By"
You open the associated language file on your site: /language/xx-XX/xx-XX.com_jamegafilter.ini (xx is your language code)
COM_JAMEGAFILTER_SORT_BY="your desired text here"