Configuration option for disabling automatic browser language detection

**Is your feature request related to a problem? Please describe.**

The default language detection based on the browser language should be configurable per instance. Some users have their browser languages in English for one reason or another and they feel it is confusing that the Decidim site's language shows up in English when they are trying to go to a Finnish site.

This may be also bad for SEO since the exactly same URL can show content in different langauges, depending on which language was detected for the bot. This would be also fixed in case proposal "Multilingual URLs for language versions" was implemented.

**Describe the solution you'd like**

I would like a configuration option which allows a system administrator to decide whether to use the automatic browser language detection or not. This way, both kinds of organizational needs could be served.

**Describe alternatives you've considered**

Only way I can think of serving the need would be through Decidim customization.

**Additional context**

Somewhat related to the following proposal:

Multilingual URLs for language versions

**Does this issue could impact on users private data?**

No.

**Funded by**

No funding available currently.