Upgrader forgets language override

[m4z]

Description

I recently attempted to do an upgrade of my "nightly" test forum, which I last did around May (:roll_eyes:). The upgrader detected outdated language files and gave me the option to use a ?lang=english (or similar) override, but a couple of "Continue"s later, it threw that URL parameter away and I was back at an inconsistent mess of english and translated strings.

Steps to reproduce

1. Have outdated language files
2. Click the upgrader link to "use/try english instead"
3. Continue through the upgrade
4. At around step 4, substep 1, the parameter is gone from the URL and there's non-english strings.

Environment (complete as necessary)

• Version/Git revision: HEAD
• Database Type: postgres
• Database Version: 9.4 (yes, the upgrade later failed for that reason; only 9.6+ is supported)
• PHP Version: 5.6.something

[jdarwood007]

This should be resolved with #8652 as we rewrote the logic.