Follow up on d0a4b20d36
The `lang` at this step is compared to the locale `code` (eg. fr_BE) so the
split is a mistake.
To reproduce the issue:
- change the language of a website to fr_BE only
- allow free signup
- register as a new user
Notice how the language of the user is set to en_US before this PR instead of
fr_BE as it should be.
closes #63616
closes odoo/odoo#64089
X-original-commit: ba21dadf17ba96ecbba917f666a3b385d9b9fd5e
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>