As I see it, language setting is currently stored in browser cookies. I just checked it - I've set language to English, logged in in another browser and it's Russian again (by default?).
I suggest to store default UI language in users profile. This setting should have preference over projects default language.
Possible use case:
1. User logs into any UserEcho project for the first time (email+password, or any OpenID)
2. Screen dims, UserEcho shows a popup window "Default language". The window has a table (wrapped list) of language options. Every option is a text label plus country flag, acting together as a toggle/radio button. All buttons are in one logical button group so that only one language can be selected. By default, users detected language is selected (query browser/OS). Window title is also displayed on detected language (e.g. "Язык по умолчанию" for Russian). The window also has a label "You can change the language in Settings later" and Save button at bottom.
3. User clicks language option, then clicks Save.
4. UserEcho stores language selection in users profile, and uses it when user logs in again.
This sample use case also requires profile settings page to have language selection.
An option to save preferred language for separate UserEcho projects could also be considered.