Describe session-based language switching in docs

[chillu]

Migrated from http://open.silverstripe.org/ticket/7044

Followup from #7041

The "Switching languages" section mentions the ?locale= GET param, and using that param would only show links to pages in a certain language. But some pages are statically linked, e.g. Security/login. Describe how to work around this by using session based locales through init(). Also fix usage of Translatable::set_reading_locale().

[Zauberfisch]

this was just topic of conversation in IRC, and I took a crack at it, in the following gist is the work around I came up with.

https://gist.github.com/Zauberfisch/9226142

I simply hook into controller init and use session to remember the locale.
additionally the extension also provides a method to generate a list of languages this website exists in.

[tractorcow]

@Zauberfisch Apologies for not looking at this in depth, but do you think it's worth migrating some of that initialisation into a RequestFilter? See https://github.com/silverstripe/silverstripe-framework/blob/3.1/control/VersionedRequestFilter.php for how Versioned does this.

I plan on using the same design pattern for the Fluent module once I get some time. :)

[Zauberfisch]

hmm, what would be the benefit of hooking into preRequest() instead of onBeforeInit()?

[tractorcow]

It wouldn't require a controller instance to do the initialisation of the locale. Probably... :)

It's also supposed to be the 'correct' way to do request-based pre-setup and post-teardown initialisation.

[maxime-rainville]

Unfortunately, Silverstripe CMS 3 has entered limited support in June 2018. This means we'll only be fixing critical bugs and security issues for Silverstripe CMS 3 going forward.

You can read the Silverstripe CMS Roadmap for more information on our support commitments.