Language neutral login.

[leymannx]

Closes #524

[leymannx]

Tests failing due to some Drush-related issue:

$ drush --yes --root=$PWD/drupal site-install --db-url=mysql://travis:@127.0.0.1/drupal
The program 'drush' is currently not installed. To run 'drush' please ask your administrator to install the package 'drush'
The command "drush --yes --root=$PWD/drupal site-install --db-url=mysql://travis:@127.0.0.1/drupal" failed and exited with 127 during .
Your build has been stopped.

[leymannx]

Ah yo, now I found out this actually would be the start to make https://behat-drupal-extension.readthedocs.io/en/3.1/blackbox.html#override-text-strings needless. Which probably shouldn't happen in v3 anymore. But maybe in v4.

I guess this PR can get closed then. And I'll have a look into the v4 branch. 😃

[pfrenssen]

True this would make the password_field and username_field text overrides obsolete. I think we can deprecate it though so this could possibly still be a candidate for 3.x which is still supported.

We do prefer changes to be made first for 4.x and then backported to 3.x.