format explanation of x, xx, x0, x_in_x0, xxx, x00, x_in_x00, xx00, xx_in_xx00, x000

[MrTheBarbarian]

Hello!
I'm trying to make translation to bulgarian.
I need info and if it is possible examples of information which have to be formatted and how have to be look like after formatting.
I started with date_time.json in res/text/ru-ru/ and I need help with interpretation of:

"decade_format": {
"1": {"match": "^\d$", "format": "{x}"},
"2": {"match": "^1\d$", "format": "{xx}"},
"3": {"match": "^\d0$", "format": "{x0}"},
"4": {"match": "^[2-9]\d$", "format": "{x0} {x}"},
"default": "{number}"
I will do my best to not asking for stupid questions, but I'm really motivated to make this.
thanks a lot!