Hi,
while translating to czech, I spotted several bugs
a) two CSS positioning/overflows problems
b) in Calendar template, usage of $txt['to'] in different context. Originally it's used in context as 'to (person)', but here it's as range preposition between two dates. These two need different strings in my language.
In Bug Reports (https://www.simplemachines.org/community/index.php?board=137.0) or (preferably) creating an issue in GitHub (https://github.com/SimpleMachines/SMF/issues/new?assignees=&labels=&template=standard_bug.md).
Make sure to keep one bug per issue on github so they can be tracked properly.