1. When I use the SCLogin with the spanish language, the login button is too long. Is there a way to fix this (see attachment)
2. After the user login: Is there a way to center the module (text and button) in the area?
This sounds like it could be accomplished by some CSS changes. I'd recommend
making your own theme
for the SCLogin module and putting any changes there. If you provide a specific URL, I could inspect your page and give you a quick suggestion for styles.