Behat: Sanity check major supported languages

[chillu]

Switch to top ~15 languages in admin/myprofile, confirm some string in that language shows up. That'll catch any errors where the YAML parser fails to parse, which happened a couple of times before.

Also test some a JS-based translation to ensure that subsystem works, e.g. the "you have unsaved changes" notice when you navigate away from a page with changes. One language is enough here to check the JS operation.

No need to test all different UIs in all languages, too much processing overhead.