Probably bug in Navtweak versions 2.6 and 2.7:

I use this http://www.xoutpost.com/168319-post142.html instructions to change language in navboot using navtweak.

In para 16 i replaced old language module with new module (with correct crc) using righ mouse click "replace". Then i saved NAVBOOT to a new file. After reopening new NAVBOOT all changes were lost. Sizes of old NAVBOOT and the new NAVBOOT were the same. Sizes of lang modules in navtweak before and after changes were the same. Text in "Strings" tab doesnt changed. No changes have occurred!

But i find workaround on this:

We cant use "Export" "Import" buttons in "Strings" tab to change any language to any.

I used:
Navtweak 2.6 and 2.7
gtk-2.10.11-win32-1 libs
BMW Navigation Operating System: V29.1
bmw x5 (e53) mk4