The easiest way to contribute is the shared Google Sheet
You can also edit the words in JLearnIt and save the file (File -> Save As...).
When you have changed many words, send it to anthony@jlearnit.com
If the user interface is too difficult to use, copy the language in Excel, Libre Office or Google Docs and add/edit the words in there.
To import the vocabulary to the spreadsheet, unselect View -> Show Gender and copy paste from JLearnIt to the spreadsheet
If you want to help complete the grammatical gender of the words (masculine/feminine/neuter), copy the language in a spreadsheet (Excel, Libre Office or Google Docs) and add a column with the gender. Then send the file at anthony@jlearnit.com.
Copy the English language in a spreadsheet (Excel, Libre Office or Google Docs) and add a column with the new language. Then send the file at anthony@jlearnit.com or do it in the shared Google sheet (See link above)
JLearnIt is not only to learn new languages but also to learn anything that can be represented in table (See File -> Starting File).
Use either File -> New menu or create a spreadsheet.
Also if you save a existing file like morse, you can edit it with a text editor, the text format is quite simple.
Even if you don't speak another language, you can also contribute by informing other people about this software. For example, send a tweet, share on Facebook, post on a forum, tell friends, colleagues or classmates about it.