I don't think you actually need different locales, because you have just balances in different currencies. You can simply pass additional arguments to number_to_currency. Something like this:
number_to_currency(70000.00, :unit => "€", :separator => ".", :delimiter => " ", :format => "%u %n")
This will display: € 70 000.00
Additionally it seems that you can set :locale option when calling number_to_currency. It's not documented, but here is the part of the number_to_currency code:
defaults = I18n.translate('number.format''number.format', :locale => options[:locale], :raise => true) rescue {}
currency = I18n.translate('number.currency.format''number.currency.format', :locale => options[:locale], :raise => true) rescue {}
So you should be able to do something like:
number_to_currency(70000.00, :locale => :ru)