Localization through options doesn't work

[uliska]

As I posted on this tex.stackexchange post I couldn't override the invoice labels through \invoiceoptions or invoice2 package options, always receiving unknown-option errors.

Looking in the translations manual I did make it work by manually using \DeclareTranslation for the labels I want to override.

After that I looked into the source code of invoice2, and although I don't fully understand the syntax I'm quite sure that you should define these variables as keys in the \keys_define:nn {invoice2} clause starting here.

As said I don't fully understand the syntax, otherwise I'd have created a pull request.