I have solved that. If someone help this:

      <t t-esc="'{0:,.2f}'.format(int(line.credit))" />

you don't need to hard code your report with a specific format. so you can use the built in formats of odoo to support multi currency. as the following example

<t t-field="line.credit" t-field-options='{"widget": "monetary", "display_currency": "o.currency_id"}' />

also you need to check & make sure about the following settings that match your need

Settings -> Translations -> Languages -> 'your language settings'

seperator format should be something like [3,0]

for more info go to http://openerp-server.readthedocs.org/en/latest/06_ir_qweb.html