Hi Peet,
Thanks for this feedback. As you noted TruClient IE does not support the browser language settings. In fact, TruClient IE does not apply any of the current IE settings to make it its' own. It uses a different registry branch that describe the settings.
Your request is suitable to be raised as Enhancement Request.
As a possible workaround (didn't test it on my own) I suggest you search for AcceptLanguage value in your registry, copy the data from this key and create the same value under TC IE browser settings which is located here:
HKEY_CURRENT_USER\Software\Hewlet-Packard\TruClient\TruCLientIE\TCIE
Regards,
Shlomi