Currently, the only message for localizing the block log entries is [[MediaWiki:Blocklogentry]]. The parameter $2 can be different values here:
*either a timeframe, like 5 days, 6 months
*a date, for example "2010-01-01T00:00:00"
However, often there isn't one word combination that fits them all, even in English. The first one should be "blocked $1 for a timeframe of $2 $3". The second should simply be "blocked $2 indefinitely $3", because "for a timeframe of indefinitely" just sounds bad. The third one then should be "blocked $1 until $2 $3". Thus, this one message should be splitted into these three different messages.
Another problem is that the time isn't properly localized. If an admin decides to block someone for an unusual timeframe and writes "6 minutes" into the form, then "6 minutes" will not be localized in the block log entry. The same goes for dates, which are always in the YYYY-MM-DDTHH:MM:SS format, even if that's not the user's preferred date format.