I asked the same question in another topic but got no answer yet. This is how I did it but maybe (I hope) there is an easier way.
Open Oxwall database (via phpmyadmin)
Click on base_language_value
Search for an unused value, I used the ning-links but there's a lot of other junk to be found like test, test1, eee, aaaa, dddd and so on.
Edit that value to what you want blogs+main_menu_item to show on your site.
Important: remember te keyId you edited
Click on base_language_prefix
Remember the id of the prefix blogs
Click on base_language_key
Find the entry with the keyId (id) from step one, the value you edited
Click on Edit
Change the prefixId to the number you found in step 2, the prefix for blogs
Change the key to main_menu_item
Go to you site via FTP
Find blogs.xml
Add a line: <key name="main_menu_item"><value>what you want to show on your site for this key (the value you entered in your database in step 1)</value></key>
Save
Find lang_#.php
Add a line: 'blogs+main_menu_item' => 'what you want to show ....',
Save
That should do it.
Note: if you have more than one active language you should also check base_language in the database for the id number of the language you are editing. The value you edit in step 1 must be one with that languageid.
It's also the number of # in lang_#.php you have to find via FTP.