To see how to enable translations have a look at "Enable translation" paragraph.

BEdita translations are located in bedita-app/locale folder and each language package consists of a folder named with relative ISO-639-3 codes. The structure is:

bedita/bedita-app/locale/(lang-code)/LC_MESSAGES/default.po

where default.po is the translation file. There are two methods you can follow to create your translation: in each method you'll have to edit a po file. Unless you're familiar with their format you should use a po editor. There are free tools such as PoEdit which make editing and updating your po files an easy task but if you want use your favourite text editor assure to use UTF-8 to avoid problems.

Method one (shell script)

To work properly this method need gettext utilities installed so if you don't or you can't install it read method two. 
As first thing you have to prepare your language .po file with a correct header entry (UTF-8 charset is important).

So for example if you want create a russian translation you have to create a file named default.po in bedita/bedita-app/locale/rus/LC_MESSAGES folder. Then you will need to edit the file headers entry. Copy them from bedita/bedita-app/locale/eng/LC_MESSAGES/default.po file:

msgid ""
msgstr ""
"Project-Id-Version: BEdita 3\n"
"POT-Creation-Date: 2011-01-04 16:26:49\n"
"PO-Revision-Date: \n"
"Last-Translator: \n"
"Language-Team: Bedita I18N & I10N Team\n"
"Language: \n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=2; plural=(n != 1);\n"

Save file, then open a shell, go to bedita folder and write:

./cake.sh gettext update

this shell script will update master.pot file and all default.po file in locale subfolders. You will see also a translation percentage for any language. This script mantains updated every language adding new entry to translate or remove entry no more used.

Once the script runs edit your default.po file translating every msgid entry with relative msgstr.

Method two (copy by hand)

Copy bedita/bedita-app/locale/eng/LC_MESSAGES/default.po in your translation folder and edit every msgid entry with relative msgstr.

Remember to use UTF-8 charset to edit po file.