Done everything, they still track me?

OK, maybe not EVERYTHING but I’m surfing the web on Fedora + Mullvad browser (standard settings, no custom blocklist) + non-Mullvad VPN with kill-switch. Problem: some popular sites (streaming, chat-bot etc) show me interface, login pop-up or google SSO, in my NATIVE (non-English) language like they can track me regardless of all my setup. I rarely use these sites but they keep me thinking. how can they do this? I just tested with Tor (standard settings) too, FIXED, showing sites in random languages (maybe its German, derived from Tor exit node). Is the VPN leaking my IP? I have checked some browser fingerprinting/IP/DNS/WebRTC sites, didn’t notice anything out of ordinary. What should i do?