There is no proper currencies list in Financisto(yet), but it was designed this way. There is no need to have all currencies in the world – you can add whatever currency you’d like, even imaginary
by yourself.
Tap Menu->Currencies, then Add button:

Fill the Name, Short name and Symbol. You should use international standard Currency Code as Short Name if you’d like to use automatic rates download available for that currency. Tap on ’Is default’ if it’s the main currency you use.
Tags: financisto

Is it possible to allow manual definition of currency conversion ?
It is not yet available, but it’s been in our todo list
Rates download for Belorusian ruble don’t work.
System.ArgumentException: Cannot convert BYR to Currency
You’re right.. Seems like the web-service which is used to provide the rates doesn’t support BYR. I’ve submitted the bug. Will check later if they fix it.. Thanks!