Steps to replicate the issue (include links if applicable):

• Go to https://idm.wikimedia.org/signup/
• Create a username that contains multiple spaces

What happens?:

• The automatically generated Unix username contains the same spaces

What should have happened instead?:

• The spaces are converted to dashes, as spaces are not valid in Unix usernames.

Software version (skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):