I know many people who first use Google Indic Transliteration to convert their posts from English script to Hindi(and other languages) and then do copy paste.
Writing Blog post in Indian Languages such as Hindi, Bengali, Malayalam , Gujarati, Punjabi, Tamil, Kannada, Telugu etc on Free Blog services is not a big deal at all as you just have to change the language settings to do that.
But if you have a hosted Wordpress Blog then again you’ll have to transliterate your post and then paste it if you are using UTF encoding which is by default switched on in Wordpress Blog.
To get started just download, install and activate this Indian Language plugin from Monusoft based on your language. Currently it supports 8 Indian languages that are – Bengali, Gujarati, Hindi, Kannada, Malayalam, Punjabi, Tamil and Telugu.
Once you are done, now when you start posting you’ll have small option to switch between Your Language (F12 as shortcut).

Write Comments also in Indian Languages
Yes, with this plugin it is possible to write Comments also in these 8 Indian Languages.
Also if you want to see the character mapping , then click on the Show Keyboard option. It’ll display you the character map which will be like this -
What if I have Free Wordpress Blog
For free Wordpress Blog just go to Dashboard Settings –> General and then change your Language from the drop down box there.
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Yes Copy and paste the translation . Can this affect you since it is copied. As in Duplicate Content even though it is Original because it is Copied from one page to another