@Petr, good question.
My goal with using the #time function was to make future re-uses of the message as simple as possible, by not requiring any updates from individual translators whenever it next needs to be sent.
Yes, that is indeed a good idea, definitely better than using untranslatable English date or something like that! The only issue is the used format.
I had thought this method would work (if not perfectly, then at least well enough for each reader to understand it).
Yeah, I believe the readers should understand the result all right, it’s just that it’s obviously non-Czech, it reads artificial/strange.
If you/anyone knows of a better way to achieve this goal, I'd be happy to learn and use it!
I thought marking the _format string_ for translation _might_ work? I. e. let the translators translate the “l F d H:i e” string inside the #time invocation; e.g. for Czech, I’d translate that to “I j. xg. Y, H:i e”. (It might need an explanatory documentation for translators – do translatable pages support /qqq documentation?) But I don’t know, does translation work inside parser functions, or will it break somehow?
Even though MediaWiki does know the proper date/time format for every language (and allows the user to select his/her preferred), it uses these for outputting timestamps on e.g. history pages (or formatting the ~~~~ signatures). But I don’t think there is a magic word / parser function / something which would provide this information into wikitext? (Yeah, the user-configured option cannot be sent to the parser, as it would break caching, but at least the default format for the content language? I guess not.)