Hi @Christop
I agree us Americans always have to tend to do things in a non-standard way such as metric or IBAN 
for better or worse we are “stuck” with what we have so far until we can move to more international standards, but that’s a whole other topic.
I absolutely agree that Bitwarden should be accommodating to ALL users from any background and nationality. Bitwarden has been translated into many local languages with the help from our wonderful community members.
So any features that will help further adoption of Bitwarden and good password hygiene worldwide I think is a valid addition to look at.
In regards to not using IBAN, we tend to use a convoluted method of routing numbers + account number. Where the account number is clearly for the account in question, and the routing number is for the specific financial institution nationwide I believe.
As far as getting involved, I’m sure that Bitwarden would be more than happy to assist with any questions you may have to help contribute.
Of course any additions will go through a standard review and QA process and carefully vetted before being accepted into the main code-base. For further detail and reading check out the contributions section in the community.
Love to see the beauty of open-source and people constantly making things better for all 