Requirements:

Setup your system for Bangla. Install OpenType Fonts and a way to type Bangla. How you want to type Bangla is upto you. You can use Yudit , Lekho or something like gedit. If you want to use gedit then you will have to setup the Bangla keyboard.
Note: You can check the documents section of Ankur's web site for installing fonts and/or keyboard.

Choose the module:

Ankur's GNOME translation project's status page has a table with all the core GNOME modules we are currently translating. The table also shows who is translating what. Choose a module you want to translate and no one else has started working on, and download the .pot file for that module (this can be done by clicking on the name of the module in the table). Please, send a note to the translation mailing list stating that you picked up a .pot file. So, we will know who is working on what.

Edit the pot file:

First you need to change the header of the pot file. To do this open the pot file with your choice of editor. On the top you will see the header of the pot file. Please take a look at the glib's translated .po file to see what to do with the header.

Now you start translating! Below the header you will see a list of strings in English, something like this:

#: libgnomevfs/gnome-vfs-result.c:36
msgid "File not found"
msgstr ""

#: libgnomevfs/gnome-vfs-result.c:37
msgid "Generic error"
msgstr ""

#: libgnomevfs/gnome-vfs-result.c:38
msgid "Internal error"
msgstr ""

#: libgnomevfs/gnome-vfs-result.c:36
msgid "File not found"
msgstr "ফাইল পাওয়া গেল না"

#: libgnomevfs/gnome-vfs-result.c:37
msgid "Generic error"
msgstr "সাধারন ভুল"

#: libgnomevfs/gnome-vfs-result.c:38
msgid "Internal error"
msgstr "অভ্যন্তরীন ভুল"

Few pointers:

While translating, remember not to kill the language. Do not overdo the translation - do not use 'Sadhu Basha'. Also, when the computer is addressing the user, it is 'samman-shuchak' (karun, balun, etc) while the computer is addressed by karo, balo, etc. If a Bangla equivalent sounds too out of the ordinary -- keep the English word (in Bangla script). It can be always changed/improved later. DO NOT overdo anything.

Use the more common word (jaanlaa and not gabaakhya). Also always remember that the words need not be very much applicable to the actual action - an Englishman from the nineteenth century could not even have guessed what "Save" can do in a computer ;-).

Also ...last but in no way the least, spellcheck, spellcheck, spellcheck. During translation session - always sit with your dictionary, or even better, the Bangla Baanaan Abhidhan from the Bangladesh Bangla Academy. The bspeller from Ankur may be used here.

Submit the pot file

Once you have translated more than 50%~60% of the pot file, send it to gnome-translation@bengalinux.org. This way other translators can comment on your work, and this feedback is very useful. You can change your translation based on this feedback and re-send the file. Remember you may have to go through this feedback cycle more than once.

Also you are encouraged to comment on other translator's work. Once someone sends in their translated po file, if you have comments or want to propose alternate translation regarding a certain translated string, please add it to the po file below that translated string commented out with a "#" and send it back to the e-mail list.