A problem with Russian language using 26.00fw

Hello everyone :)
I've found a very strange issue after upgrading to 26.00 firmware - firstly I noticed that every Wednesday the weekday name is missing or shown as 'questionmarks'. (Affects watchfaces, widget menu and calendar)
So I began to investigate how to fix it or at least to narrow the possible failpaths.
Here are my findings:
It happens only on Wednesdays, other weekdays are displayed correctly;
It happens with every full and abbreviated writing of Wednesday in Russian (Wednesday, Wed, WED, WD, etc.)
It happens only with Russian language, weekdays in other languages always displayed correctly;
Full factory reset from the system menu doesn't help;
Full factory reset using long-press of buttons doesn't help;
If replace Russian symbols 'СР' (unicode U+0421, U+0420) with similar-looking English-ones 'CP' (unicode U+0043, U+0050) in the language files, also doesn't help.

Widget menuCalendarCalendar2

Later I've found a similar issue under "System/Format/Pos.Format/Format" - if system language is Russian then some options' names are corrupted, this behavior doesn't correlate with weekdays and persists all the time.

RussianFormatEnglishFormatRussianFormat2EnglishFormat2

Could it be resolvable by myself, or the only option is to wait for a new firmware and hope that this bug will be fixed?
Thanks! :)