Originally Posted by louigi600
A bit off topic but in response to a question ... hope it helps:
You can do it from the command line with iw: (you're form Germany so I'll give you German reg examples)
iw reg set ISO_3166-1_alpha-2
iw reg set DE
If you use wpa_supplicant you can add this in there (and have different ones for each configured wifi network)
In practice if you use crda (and slackware does) you're not going to gat any more channels than what the domain that your wifi card was marketed for has, even if you totally disregard the reg domain stuff. If by any change you buy via internet from one of the countries with less restrictive domains that the country you plan to use the card in you might want to set the correct domain to operate within limitation of your country.
Way back in the early days when regulatory domains were introduced I used to tinker with the kernel source to set the default to JP (the less restrictive domain) but things have gotten more complicated over the years and I gave up on that approach. But maybe it's still possible to alter the default world "00" region on linux/net/wireless/reg.c to look like JP ... but to get that to work you need to disable crda (else it will limit the chanells to whatever is is set in the firmware set reg domain of your card). One could try dissuading udev from running crda and see how that works jointly with tinkering with kernel source. Be warned that this may be illegal in some countries.
Many thanks for your detailed answer David! My bad, I should have also written that I had searched for it and had found the solution on this very site. For others that might be led here from a search I will add one more solution just for completeness' sake:
Create a file in /etc/modprobe.d/ with the extension conf, for the Raspberry Pi's build-in wifi card that is driven by the brcmfmac module it should read (for example for my Germany region):
softdep brcmfmac pre: cfg80211
options cfg80211 ieee80211_regdom=DE
About the regulatory differences: That was in most parts new to me, thanks. A quick search didn't show me a clear "winner" between German and Chinese (that was what the kernel or whatever it is selected as the region before) regional settings. Maybe I will try both and experiment, if the connection is becoming better. Could be the case If ever I will get a router with 5 GHz capabilities.