Every 30 minute…s

Speculation: the string is possibly written with FormatString(unit == "minute" ? Strings.EveryMinute : Strings.EveryHour, value) + (value == 1 ? "" : "s"), i.e. a template exists for “Every � minute” and “Every � hour”, with plurality handled by mechanically appending a letter “s” to the end of the string in the English way.

It is common to see this “add-an-s-if-not-one” pattern in applications hardcoded in English, but rarely observed in localized ones.