The front end language file /language/en-GB/en-GB.com_bfauction_plus.ini contains the text used in the auction for buttons, error message etc. If you want to translate into your own language, copy the English language file into /language/nl-NL/nl-NL.com_bfauction_plus.ini (where nl-NL is your language).
Each line of your language file will be in the format:
If you would like your language file to be included in a future version, please feel free to get in touch via our contact form.
If you would like to make minor changes to the current language files, it is better to create language overrides rather than edit these language files directly, that way you will not have to reapply your changes each time you upgrade the software version.