From the documentation:

How display language is determined

Existing end users (activated) — Okta evaluates these sources in the following order to determine which supported language is displayed to activated end users in their Okta instance:

1. End user's Display Language setting. See End users: set up display language.
2. Cookie that holds the web browser's current language setting. Relevant in a shared-terminal scenario where multiple operators use the same browser. The browser displays in the language that the most-recently authenticated user configured in their Okta End-User Dashboard > <username> > Settings > Display Language assuming they've configured a display language.
3. Language configured in the browser settings.
4. Value of the user's locale property.
5. Org-wide display language is displayed to all users unless overridden by any of the preceding sources.

Is this a match & quit type of eval or does it go through all steps and keep the most recent match (with the exception of *5)?

IE: user with Display Language set to English, first login so no cookies, French browser, locale not defined.

Do they get French?

Thanks