Change 111204 had a related patch set uploaded by Manybubbles:
Handle space in namespace prefixed searches

https://gerrit.wikimedia.org/r/111204

Patch handles first case but not others so setting back to assigned.

Change 111210 had a related patch set uploaded by Manybubbles:
Trim quotes from prefix: search

https://gerrit.wikimedia.org/r/111210

Neither of the patches on this bug handle the last issue but I'm not actually sure what the user thinks is wrong there so I've gone back to them on the talk page at https://www.mediawiki.org/wiki/Thread:Talk:Search/prefix:_search_for_localized_namespaces_broken/reply_%282%29

Change 111204 merged by jenkins-bot:
Handle space in namespace prefixed searches

https://gerrit.wikimedia.org/r/111204

Change 111210 merged by jenkins-bot:
Trim quotes from prefix: search

https://gerrit.wikimedia.org/r/111210

Looks like the last point wasn't really a bug, more of a feature request that is unfortunately complicated. I'm happy to be wrong, in which case I'll open another bug. For now, though, I'm marking this one resolved.

mr.heat wrote:

(In reply to Nik Everett from comment #4)

last issue [...] I'm not actually sure what the user thinks is wrong there

You are right, the last issue doesn't make much sense since it could mean two things: Search in that namespace or search for articles with that prefix. I think it's more sane to do the later.

Thank you very much for the fixes!

Thanks for working patiently with me to get the changes figured out and for verifying them!