UI language of Red Hat Web pages goes crazy!

The Web interface of RHN, RHSM, and RH Customer Portal has its language going crazy:

1. Language changes randomly:
   No matter if I switch between pages or refresh the same page, no matter if I let the language be default or intentionally chose a language on menu, I usually see the displayed language changes randomly, and uncontrollably.
   I've check the request cookie and it correctly reflects my choice of language: If I let the language be default (from a fresh restart of browser) then no "rh_locale" entry is defined; If I chose one language on the menu, the "rh_locale" entry in the cookie reflects my choice. However the displayed language is nondeterministic!

2. Inconsistent languages between Headers (Products & Services, Tools, Security, Community), Utility bar and the Main body content:
   For example when Japanese is chosen and displayed,

   • https://access.redhat.com/errata/RHSA-2017:0170 shows English headers, English unitility bar (with "English" is displayed as the chosen language in Language menu), and Japanese body content; while
   • https://rhn.redhat.com/errata/RHSA-2017-0170.html shows Japanese headers, Japanese unitility bar (with "Japanese " is displayed as the chosen language in Language menu), and English body content.
     *) As described in number 1, the chosen language is not always the displayed one.

==> I want a consistent language through out the time. Is there any way to constrain the Web pages to display only English?

Update on June 28th: Thanks to Sam Wachira's suggestion about the Locale preference, I've re-tested the RHSM Web UI with stable result when logged in & locale preference set. But right after I logged out, the UI language went back to random behaviour. Here I upload an archive of screenshots of each step in my test:
- 0x: Open erratum RHSA-2017:0244 in a new (fresh) browser (Google Chrome). Just refresh ==> random languages;
- 1x: Choose "English" ==> still random languages;
- 2x: Log in & set locale preference (language = "English") ==> seems to be stable!
- 3x: Log out ==> back to random!
- 4x: Log in & 5x: set locale preference language = "French" ==> seems to be stable!