Extra personalization of internationalization

[arte-dev]

What this PR does

Allow to modify lookupCookie for i18next. This is in line with current implementation, but it certainly would be better if all options could be overwritten. This is needed to be able to take advantage of the existing domain cookie that manages the language

Test me

Use cookie on changeLanguageOnStartWhen and change lookupCookie to the desired value. Change the language and you'll see the proper value on the cookie with name lookupCookie

Checklist

• [x] Unit tests aren't applicable,
• [x] I've updated relevant documentation in doc/.
• [x] I've updated CHANGES.md with what I changed.
• [x] I've provided instructions in the PR description on how to test this PR.