Unfortunately, there has been no reply from either of the stack developers yet. After searching a little bit more on this topic, I stumbled across a response from @tav in a different forum (Limelight & RWML), where he explained that RWML stacks work only well for content replacement, but css or JS code isn’t dynamically changed possibly leading to problems with more complex stacks.
This is very likely the case for the Kalendar stack, where events are dynamically shown on the left side when a respective date is picked. Though way outside my ‘comfort zone,’ I tried to use the browser inspector to look at the JS scripts and the generated HTML code - there indeed seem to be references in the script to pages not available depending on the language setting (but this also seemed to be the case on the main page with both calendars visible, so what do I know ;).
In this context, however, another idea crossed my mind - and I could use some help to test whether it is possible to get it to work: instead of using the PHP server side exclusive loading of different Kalendar stacks, load them all (like on the main page in the example), but make only the stack with the proper language visible. According to @willwood RWML support page a standard language tag (e.g.
<div lang="de"> ... </div>) should work with RWML suppressing the display for inactive languages.
Though not sure whether it solves my problem, I would like to try it, but already stumble with the basics of mixing stacks with direct HTML code: How could I add the
lang="de"tag into the div of the Kalendar stack. Or how could I enclose the respective Kalendar stacks into divisions with the lang tag ?
Thanks anyone for helping, cheers.