Hi Vaclav,
Unfortunately, it is not possible to localize the calendar settings for the current version of the chart.
Since this feature has not been actively requested and is not a priority at this point. What we can offer is that you can request a paid feature development (via co-financing it). This is the way to accelerate new features.
Would you be interested in co-financing it? This paid feature request would cost $299.
Thanks,
Aivis Pavlovs