Formatting with Powershell

Hey there!

I'm currently working on a script which should prepare a xml-file for a import into a pdf-form.
Now I need to format some digits in the xml tags I defined.
The formatting part looks like this:

if( [int32]$_.innertext -lt 0) {$_.innertext = "(" + '{0;0,0}' -f [int32]$_.innertext + ")" } else { $_.innerText = '{0:0,0}' -f [int32]$_.innertex }

Now I'm aiming for this result:
If in the xml Tag the number is 1000000 -> it should make 1'000'000 out of it
if its -1000000 it should make (1'000'000)  out of it.

Well, I'm kinda pretty close to a solution for it - on my machine.. my machine-culture is currently  set to en-US, so i get 1'000'000 and (-1'000'000) with these formatting. but. The script need to run an a de-CH (other number formatting than en-US!) machine.

Does anyone have a clue how to do this? Can't I define a "better" integer formatting?
I have a feeling the culture-settings are to deep into this.

Best Regards