If you hit the home button twice, then up once, then right once, up once, right once, then down four times, you should be in the language settings menu. If they are in the same order as my Ultra 4640, English is three up from French.
If that isn't working, then I suggest a hard reset and set it up from the beginning again.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.