Without an English language pack, you could not be sure that an interactive program provided an English interface. Besides there are many versions of English – I would get fairly frustrated if I was forced to use e.g. US, Belize or South African locales.
Better protect that wild card for zypper from shell interpretation:
zypper al '*-lang'
While it might not be very likely that there is one or more files that fit this path expansion, the chance is not 0%. And when this way of using wild cards for zypper becomes a habit of people reading this, sooner or later they will experience “strange things happening”.