There's been an ongoing thread on the forums with people reporting that community forum pages show in the wrong language.

This has happened to me today and I was able to capture the HTTP headers which may help identify the issue. My browser's locale is en-GB, I'm in the UK, and my moodle.org profile's preferred language is "English (en)". This is the request:

GET /mod/forum/view.php?id=28 HTTP/2
Host: moodle.org
User-Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Referer: https://moodle.org/mod/forum/discuss.php?d=436125
Cookie: _utma=43082041.356681913.1638957166.1657184545.1657199992.393; __utmz=43082041.1657104423.389.37.utmcsr=duckduckgo.com|utmccn=(referral)|utmcmd=referral|utmcct=/; local_plugins_moodle_version=37; cf_clearance=U0vSaPOKqdvd4QglwYa05ZzxR3R_Le_zaeS9HQfcG6M-1657115452-0-150; _ga=GA1.2.356681913.1638957166; EU_COOKIE_LAW_CONSENT=true; MoodleSession=3240991566354277284cf2941af88954; __utmc=43082041; MOODLEID1=%25FA%25F5%2592%252C%25AE%25C5O; __utmb=43082041.34.10.1657199992; __utmt=1
Upgrade-Insecure-Requests: 1
Pragma: no-cache
Cache-Control: no-cache
TE: Trailers

But the forum page loaded in Haitian Creole (HAT):

HTTP/2 200 OK
date: Thu, 07 Jul 2022 14:32:31 GMT
content-type: text/html; charset=utf-8
cache-control: private, pre-check=0, post-check=0, max-age=0, no-transform
content-encoding: gzip
content-language: hat
content-script-type: text/javascript
content-style-type: text/css
expires: 
pragma: no-cache
strict-transport-security: max-age=15768000
vary: Accept-Encoding
x-content-type-options: nosniff
x-frame-options: sameorigin
x-ua-compatible: IE=edge
x-xss-protection: 1; mode=block
cf-cache-status: DYNAMIC
expect-ct: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
server: cloudflare
cf-ray: 72714a368ef071b4-LHR
X-Firefox-Spdy: h2