Glad to hear from you, Hermann!
Some more issues
Minor on localization:
info_acp_calendar.php seems to have duplicate records 'ACP_CALENDAR_EVENT_CONFIG' with different values in all three languages (de, de_x_sie, en).
The first value is lost.
While the button caption and panel title share 'ACP_CALENDAR_EVENT_CREATE' string.
More important localization : i have non-localized dates in "Upcoming dates" panel (styled with 'CALENDAR_DATE_FORM', but English one, while by board and user have working Russian locale) and perfect localization in invited person registration dates.
Registration dates are localized in main_listener.php at line 375 and upcoming dates -- at line 875.
Strange input - wierd output: In the admin panel I have created annual date, starting on January 16-th _no_year_, ending on January 17-th 2021
-- Annual 2-day events (Jan 16-th - Jan 17-th) ending in 2021 (no events in 2022 and later)
-- or may be long event starting Jan 16-th 2019, ending Jan 17-th 2022
Real: Almost everyday event, except small ranges: Jan 1- Jan 15 2022, Jan 1 - Jan 15 2023 and so on.
Special mention: 2-week upcoming dates panel showed events on Jan 1-st 1970, Jan 16-th 2020, Jan 17-th 2021, Jan 17-th 2022.
I would be happy to receive a Russian translation...
Ok, I'll email it, as soon as it is ready!