Posting as I have/had same issue.
Rubenel,
my router language page didn't change to chinese until relatively recently (last week or so).
I concur. I've been mucking around with my router for the last month on & off, & it's only just happened recently. I've recently setup & connected some IP cameras to my network, via VPN server, so my concern is around whether they're the cause. I've also downloaded some stuff recently that Norton has also flagged & removed so that could be another factor & I've been using the ASUS Router app on my smartphone too.
RT-AC3200 currently on FW: 380.69.
My observations after checking all my settings etc, some of which I don't remember what they were;
AiCloud 2.0 -> Cloud Disk & Smart Access were on. Pretty sure they weren't on previously.
PING from WAN disabled: No.
Malicious website blocking enabled: No.
Vulnerability Protection enabled: No.
Infected Device Prevention & Blocking: No.
HTTP/S: both - could have sworn I had this setup for HTTPS only.
Enable SSH: no.
Enable Telnet: no.
Enable web access from WAN: No.
VPN Server PPTP: thought I had this disabled but it was enabled.
About a week (maybe 2) ago my outbound connection stopped working. This despite everything showing 'ok' ie modem & router. I was able to connect to my home network cameras & the router itself via my smartphone via the net, so I temporarily disabled the firewall & re-enabled it, & my outbound internet worked fine. My internet connection has done this before & usually I reboot modem & router, but this was the first time I've tested incoming connection & seen a problem like this, thus temporarily disabling firewall.