By default WordBanker is intended for an English speaking person wanting to learn another language in which case the primary language would be English. WordBanker can also be used for someone wanting to learn English but the program language (GUI) remains in English so it is more suited in a family where one member of the family speaks English and is able to explain how the program works.
To change the primary language go to Tools > Options > Primary Language
In the above image, you would be learning Croatian and so the primary language is English. If your wife is Croatian and she wanted to learn English then you would click the but "Change".