* github-vse/ticket/12254:
[ticket/12254] Add subsilver2 support for cookie storage instead of SID
[ticket/12254] Use a cookie instead of SID to store language selection
[ticket/12254] No longer need to add change_lang to the URL params
[ticket/12254] Use 'language' instead of 'set_lang' as the variable name
[ticket/12254] Persist set_lang after reg only if changed from default
[ticket/12254] Add set_lang var changes to subsilver2 files
[ticket/12254] Use new set_lang var to avoid conflict with change_lang
[ticket/12254] Stop using deprecated request_var in user class
[ticket/12254] Better language switching on registration page