It’s just a common courtesy that should be given,we get one for the US in the 4th of July event (as well as a lot of smaller events) and not all the other nations do.This could be a good way to provide content for more minor nations that took part during WW2, So I’ll throw a few of those in here as well (note that I didn’t include Britain since they don’t have an official national day,otherwise I would have included them).So without further ado, here are some of the possible national holiday events for each nation,and a proposed low BR tank they can come with as an idea for them to have on said day.
the national holiday of Russia, known as Russia Day (very creative) is on june 12th,and commemorates the switch to democracy from communism back in 1991.
T-26-4
A version of the T26 with a different turret fitted to it with a low velocity 76mm cannon.This cannon heavily lacks in armour piercing capabilities compared to the 45mm cannon,only penetrating 35mms,but the HE shell has 30 grams more HE filler then the German short 75mm cannon.
Bastille day takes place on June 12th,and lies on the day of the storming of the Bastille in 1789 during one of their revolutions,and represents unity among French people.
D2
A french tank used during the invasion,has a decent,well rounded balance of armour and firepower for low BR,functioning similarly to the panzer 3J
Reunification day,started in 1990 on every October 3rd,commemorates the reunification of East Germany to West Germany,making Germany one country again after it was split.
Neubaufahrzeug
A prototype pre war tank design (this one actually saw limited service in Norway) that would be a very unique tank for Germany.This tank has 3 turrets,similar to the T28,the main turret with a short 75,a 37mm,and an MG13;as well as a front facing turret with an MG13, and one rearward facing (I hope this one gets the gunner AI on the LVT-4).you might think i’m crazy for suggesting this to be on BR1,but that’s without hearing the armour values: less then 20mm everywhere (20 is the thickest value on this thing),so thin even M13s and T60s can chew through this thing.this tank would be a high risk high reward option for low BR.
National Foundation Day is on February 11th,and commemorates the founding of Japan by the first emperor taking the throne,starting officially in 1966,but existing as a national holiday since the Meiji period (1868-1912)
Ke-Nu
Essentially an upgunned Ha-Go that uses the turret and 57mm cannon on the Chi-Ha,would be nice to get a free 57mm cannon (I still think the Chi-Ha should be TT though).
Republic day in italy is held on June 2nd,and commemorates the formation of the Italian Republic in 1946
M 14/41 (47/40)
A modification of the M 14/41 that replaces the dual 8mm MGs in the hull with a 13.2mm machine gun with a 30 round magazine.Due to the limited mag size,I don’t think this would be OP,and it would be a fun addition for Italy enjoyers
National Day in Hungary is the 15th of march,and celebrates winning the revolution and forming of Hungary against the Austrian Empire in 1848.
Turán I
A hungarian tank armed with a 40mm cannon,it has pretty decent armour similar to the panzer 3J’s ,and as well as some wire spaced armour on the sides and turret(little in game effect,but cool looking).Another unique feature about this tank is that is has a reverse gearbox similar to the Puma’s,so you reverse just as fast as you go forward.
can also be added they didn’t fought but they supplied a lot of nations and had very unique weapons that some are even in the axis gold order and 
can also receive some representation there is really a lot of option 
also Spain also had interesting weapons