sourceforge

Bash's language defaults to your system language when it's started. A specific language can be forced by using the -L switch in the command line (e.g. -L English). Setting the language via the program menu just sets the -L command line switch for the next time; it doesn't get stored. Deleting the translation files also helps. If Bash can't find your OS language, it defaults to English.

I don't think adding a new .dat for this is a good idea. Would be better to have a human-editable bash_boot.toml somewhere central (i.e. probably %LOCALAPPDATA%\Wrye Bash on Windows and ~/.config/wrye-bash/ on Linux) - that way you can edit it if WB gets your language dead wrong.
We should also use that boot INI to store the last launched game for the game select popup, that's been a long-since requested feature (that way you can just hit Enter to launch the last game immediately).

Under #500