I would like to change the content of the mail being sent after a customer completed a purchase.
Is there anywhere a manual, how to edit the mail under System -> Emails?
And is it correct, that I have to change the appropriate language template like 'ORDER_CREATION_SUCCESS_ON_WEBSITE_AT_DATE' under System -> Configuration -> Tab "language" to personalize the mail? I use German language.
Is there an overview of all these template strings?
Basically my bill should look like the bill displayed under Sales -> click on one order number -> click on invoice at the top right.
Only bank account information should be added.
If you want to change the text in the email, you should override the translations as explained there:
www.hikashop.com/en/download/languages.html#modify
Just search for the text with the search function of your browser, while you have the translation file opened if you want to easily find the text to change.
