World: r3wp

I have a general FORMAT func I use, but it's quite heavy as it handles 
a lot of things.

Thanks. The one from Nick should be ok.

You can also check

http://www.rebol.org/view-script.r?script=printf.r

I've also put a format-number function that I use on Checklists on 
Altme. It works well for me.
>> format-number 1 / 3
== "0.333333333333333"

Under Checklists / Code Snippets.

The function by Nick is a little slow since I have a lot of numbers. 
This is faster but not very fast:

format-decimal: func [x /local e q] [
	x: form x
    if find x "E-" [ 
		e: to-integer next next q: find x "E-"
		clear q
		remove find x "."
		if #"-" = first x [x: next x]
		insert/dup x "0" e
		insert next x "."
	]
	head x
]

The idea from Ladislav is nice but I would like most a more "rebol" 
solution.

Scientific notation of numbers and automatic reformating time! values 
(00:00:00 --> 0:00) are the most annoying parts of REBOL for me.
It would be more useful if it doesn't happen when FORMing.

Is there a possibility for cyrillic/Russian at Rebol/View except 
for pixelart drawing the characters?

In R3/View, but it's currently buggy and limited to Windows and Amiga

Since you'd have to switch languages anyway, you could also consider 
Red with the GTK+ binding

Uh. In Red, everything is possible with any bindings