The {CustomName} tag does not work with letters

When I tape a command such as :
/summon minecraft:armor_stand ~ ~ ~ {CustomName:"azerty"}
It says "Unable to summon entity"

but when I tape it like this :
/summon minecraft:armor_stand ~ ~ ~ {CustomName:"123"}
it works.

P-S : /summon minecraft:armor_stand ~ ~ ~ {CustomName:"123azerty"} does not work either.

And I don't know if it is a bug, but /summon minecraft:armor_stand ~ ~ ~ {CustomName:123} does not work too.

And it's the same problem with the /data command.