Missing strings for translation
There are dozens of strings not marked for translation like:
And other marked in <%trans > but missing in .po file (weblate)
When the string is not using "<%trans", it is just a matter of adding it (or will it break something elsewhere?) And it would be very important to keep .po file as update as possible. It the automatic process missing some strings? Translation contributions are opportunistic and mailman will miss that opportunity if .po is outdated.
I'm not an i18n developer expert but it might be a good way to test if the translation infrastructure is fine (like create a fake language like te_st prepending all english texts with a special character (i.e.: "§"). Whenever a string does not have it, either the string was not marked for translation or the po file is outdated.
This also affects hyperkitty.