[FIX] website: restore the language install steps in tour

Those steps were removed with [1] to avoid a indeterminist timeout, but by
doing so that part of the feature was not tested anymore.
Sadly, it was broken by [2] without being noticed for a long period of time.

The error was discovered by fixing multiple lang issues in the website
configurator in master.

Note that by creating a new lang instead of using an existing one will avoid
the timout error that lead to the removal of those steps with [1]. Indeed, as
no .po files will be found for that lang, it won't spend time on processing
those files.

[1]: https://github.com/odoo/odoo/commit/a15c7099a36a3a5b4dca9375b233cbe3fe2a280f
[2]: https://github.com/odoo/odoo/commit/745ef9de97544d5c1a97e03be67e903feca40c2a



closes odoo/odoo#83275

Signed-off-by: Romain Derie (rde) <rde@odoo.com>