[americanexpress] Correct accounts currency
Referring to issue #303 (closed)
Get correct accounts currency from users session locales rather than static so it works for other currencies than EUR.
Currently the back-end is gathering currency from a page with a static URL referring to "fr-fr" locale. So for accounts from other regions (non EEC) the provided currency is EUR instead of actual one.
Workaround is to get the proper locale from the AMEX session to get the correct config (json) package.