Request for Bugzilla
With regard to the issue with "browse" and "no file selected" unfortunately the text shown is in the browser language rather the wiki language. So if a browser doesn't have Chechen as an option then the text cannot appear in Chechen. See bugzilla 56813 for decision not to fix (too time-consuming). When I have the time I will add something on the advice to developers so that this hopefully won't happen again.
With regard to the issue with the "time-ago" messages, I note that there are a few more "time-ago" messages in MediaWiki core which you could translate:
- Seconds-ago ("
$1 {{PLURAL:$1|second|seconds}} ago") - Weeks ("
{{PLURAL:$1|$1 week|$1 weeks}}") - Years ("
{{PLURAL:$1|$1 year|$1 years}}")
I am not certain that these messages are used in the Echo extension messages (notification system), as this is still being investigated, see this thread. Please note that there appears to be a bug associated with this as well, where if the number of days, hours, minutes, etc is 1, then the message appears in English. This bug has been reported on bug 54731. So I think we need to wait while the developers investigate that bug.